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Validity and reproducibility of a food frequency questionnaire designed for residents in north China

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Abstract

The objective of this study was to evaluate the validity of a Xi'an food frequency questionnaire (FFQ) designed for application in an international case-control colorectal cancer study. The FFQ was administered to 125 participants twice over 1-year interval. Four 24-hour dietary recalls (24-HDRs) were conducted with the same participants in each season of the year. Comparative validation was assessed by comparing the nutrient intakes derived from the 24-HDRs and the FFQ-2, and reproducibility was estimated by comparing the nutrient intakes from two FFQs. In the validation study, the mean deattenuated correlation coefficients for nutrients between the 24-HDRs and the FFQ-2 ranged from 0.35 to 0.84 in the males. The female results were slightly lower than the male's. The mean percentage of classification into the same quartile was 38% for the males and 35% for the females. In the reproducibility study, the mean crude correlation coefficients between the two FFQs were from 0.41 to 0.68 in the males and from 0.36 to 0.66 in the females. The newly developed Xi'an FFQ appears to be reasonably valid and reliable for most nutrients but would benefit from the addition of nutritional supplements and seasonings for assessing dietary intake in older persons in Xi'an, China.

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... We measured the pork consumption of study participants using a Food Frequency Questionnaire [30] . Participants were asked about the average frequencies and portion sizes of 121 food items consumed during the preceding year, including the type of pork dishes that were typically consumed in the study region. ...
... Food items were grouped based on the China Food Composition 2004 classification proposed by the Chinese Center for Disease Control [31] . We previously validated the food frequency questionnaire using a 24-h diet record [30] . For pork consumption, the Pearson correlation coefficients of the validity and reproducibility of the food frequency questionnaire were 0.49 and 0.58, respectively. ...
... Given our casecontrol study design, information regarding past pork consumption may have been misclassified to some extent. To reduce misclassification of dietary exposures, we designed and validated our questionnaire using the 24-h diet record method [30] . The results showed that the questionnaire had reasonable validity and reliability. ...
Article
Aim: To explore potential interactions among Helicobacter pylori (H. pylori), CagA status, interleukin (IL)-1B-31 genotypes, and non-cardiac gastric cancer (GC) risk. Methods: A case-control study of non-cardia GC was performed at 3 hospitals located in Xi'an, China, between September 2008 and July 2010. We included 171 patients with histologically diagnosed primary non-cardia GC and 367 population based controls (matched by sex, age and city of residence). A standardized questionnaire was used to obtain information regarding potential risk factors, including pork consumption. H. pylori CagA status was assessed by enzyme-linked immunosorbent assay, and IL-1B-31 genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism. Multivariate unconditional logistic regression was used to explore potential interactions among the factors. Results: The CagA appeared to confer an increased risk of GC (OR = 1.81, 95%CI: 1.25-2.61). The main associations with IL-1B-31C allele here were 0.98 (95%CI: 0.59-1.63) for CC vs TT and 0.99 (95%CI: 0.64-1.51) for C Carriers vs TT. However, no associations were observed for CagA or IL-1B-31 genotype status among subjects who reported low pork consumption (P for interaction = 0.11). In contrast, high pork consumption and IL-1B-31C genotypes appeared to synergistically increase GC risk (P for interaction = 0.048) after adjusting for confounding factors, particularly among subjects with CagA (OR = 3.07, 95%CI: 1.17-10.79). We did not observe effect modification of pork consumption by H. pylori CagA status, or between H. pylori CagA status and IL-1B-31 genotypes after adjustment for pork consumption and other factors. Conclusion: These interaction relationships among CagA, IL-1B-31 and pork consumption may have implications for development of the preventive strategies for the early detection of non-cardiac GC.
... Dietary information was collected by a 92-item semiquantitative food frequency questionnaire (FFQ), with nine intake frequency categories, including "almost never" to " ≥ 3 times/day". Our FFQ is established and revised based on the validated Xi'an FFQ in China [13]. In validation study, the deattenuated correlation coefficients for nutrients estimated by the FFQ and 3-d 24 dietary recalls were from 0.35 to 0.85 in men, and slightly lower in men [13]. ...
... Our FFQ is established and revised based on the validated Xi'an FFQ in China [13]. In validation study, the deattenuated correlation coefficients for nutrients estimated by the FFQ and 3-d 24 dietary recalls were from 0.35 to 0.85 in men, and slightly lower in men [13]. Meanwhile, the correlation coefficients between the two FFQs in reproducibility study ranged from 0.41 to 0.68 in men and 0.36 to 0.66 in women. ...
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Background The association between dietary cholesterol consumption and dyslipidemia is still in controversy. The study aims to evaluate whether dietary cholesterol intake associated with dyslipidemia and its components in Chinese health examinees. Methods A large-scale cross-sectional study was conducted among health examinees of in Shaanxi province. Totally of 8358 participants (3677 male and 4681 female) were included. Dietary cholesterol intake was assessed by validated food frequency questionnaire. Multivariable regression and restricted cubic spline models were used to capture the linear and non-linear association between dietary cholesterol and dyslipidemia. Results A total of 2429 (29.1%) subjects were newly diagnosed of dyslipidemia, the prevalence was 29.2% in male and 27.7% in female. Mean intake of dietary cholesterol was 213.7 mg/day. After adjusting for all potential confounders including demographics information and lifestyles, higher cholesterol consumption was related to lower risk of dyslipidemia, the ORs (95% CIs) across Q2 to Q4 group were 0.87 (0.60–1.26), 0.80 (0.55–1.18) and 0.61 (0.41–0.91) in female. With further controlling for nutrients principal components, a null association was observed between dietary cholesterol and dyslipidemia and serum lipids, regardless of gender. Results of restricted cubic splines showed that the risk of dyslipidemia decreased slowly until around 300 mg/day in men and 200 mg/day in women, although the non-linear association was not significant. Conclusions The study suggested that dietary cholesterol consumption was not associated with dyslipidemia or serum lipids in Chinese health examinees, although a decreased risk was observed before the threshold points.
... In China, about half of the population live in rural areas. Though some FFQs had been used to collect dietary information in different Chinese populations [4][5][6][7][8][9][10][11][12][13][14], we did not find a reproducible and validated FFQ suited to population lived in the rural areas of southwest China. Thus, we developed a 76-item FFQ for assessing the habitual diet, and our previous results showed that this FFQ was reasonably reproducible and valid to assess the overall dietary consumption via dietary pattern method in the target rural population [15]. ...
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Background This study aimed to assess the reproducibility and validity of a food frequency questionnaire (FFQ) developed for diet-related studies in a rural population. Methods One hundred fifty-four healthy residents were interviewed with a 76-item FFQ at baseline (FFQ1) and 1 month later (FFQ2) to assess reproducibility, and required to complete two three-day dietary recalls (DRs) between two FFQs to determine the validity by comparing DRs with FFQ1. Results Crude Spearman correlation coefficients between FFQ1 and FFQ2 ranged from 0.58 to 0.92 and energy-adjusted coefficients ranged from 0.62 to 0.92; weighted kappa statistic covered a spectrum from 0.45 to 0.81, depicting moderate to good agreements. For validity, there were moderate to strong associations (0.40–0.68) in most nutrients and food between FFQ1 and DRs; weighted kappa statistic demonstrated fair to moderate agreements for nutrients and food (0.21–0.49). Conclusions The results suggest that the FFQ has reasonably reproducibility and validity in measuring most nutrients and food intake, and it can be used to explore the dietary habits in studying the diet-disease relationship in Chinese rural populations.
... L'ajustement énergétique a diminué les coefficients de corrélation pour tous les nutriments, ce qui arrive souvent lorsque la variabilité est davantage liée à des erreurs systématiques de sous-estimation et/ou surestimation qu'à l'apport énergétique (Rimm EB, Giovannucci EL et al. 1992;Malekshah AF, Kimiagar M et al. 2006). De même, d'autres études n'ont pas rapporté que les estimations ajustées sur l'énergie amélioraient les corrélations brutes (Wang X, Sa R et al. 2008;Dehghan M, del Cerro S et al. 2012). Les coefficients atténués de corrélation ont été augmentés en raison de la correction de la variation quotidienne des apports (Tableau 3). ...
... Previous studies have suggested that adjustment for energy intake increases the strength of correlations when variability of nutrient consumption is related to energy intake, but weakens the correlations when variability depends on systematic overestimation or underestimation [5]. In several other studies [7,11,[17][18][19][29][30][31], there was no improvement in the crude correlations for some nutrients after adjustment for energy intake, and systematic overestimation or underestimation is expected with the FFQ [31]. The high correlation of energy in this study was similar to the findings of another study, and the two methods used in both studies share some of the same sources of errors, such as the underestimation or overestimation (due to memory flaws) of the quantities of foods consumed, which could help explain the artificially high correlations of energy reported [7]. ...
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Background: The nutritional status of school-aged children in Cambodia remains largely unknown. No tools for large-scale assessment of daily nutrient intake exist for this population, making development of appropriate intervention strategies difficult. Thus, we aimed to devise and validate a food frequency questionnaire (FFQ) that is suitable for and dedicated to assessing the dietary intake of macronutrients and calcium in school-aged children in Cambodia. Methods: We developed an FFQ based on data from a single 24-h recall survey of 2020 children. The final list, which was developed as specified in the Block method and stepwise multiple regression analysis, comprised of 56 food items covering intake of energy, macronutrients, and calcium. We assessed the validity of the FFQ by comparison with a duplicated 24-h recall survey before and after de-attenuation. We also tested the reproducibility by comparing the first and second FFQs (FFQ1 and FFQ2) administered at an interval of approximately 6 weeks. Results: The 56 food items in the FFQ accounted for 73.3% of the dietary calcium intake of Cambodian children and explained most of the inter-individual variation (cumulative R2: 0.96). The intake estimated by the FFQ was lower than the average intake across the two 24-h recall surveys. Spearman's correlation coefficients for comparison between FFQ1 and FFQ2 ranged from 0.29 for fat to 0.47 for calcium. After de-attenuation of data, Pearson's correlation coefficients ranged from 0.38 for fat to 0.71 for energy. Cross-classification analysis indicated that the average percentage of the subjects classified in the same or adjacent quartiles was 78.0%. Conclusions: The FFQ is potentially a reliable scale for measuring nutrient intake in this population.
... Energy-adjustment decreased correlation coefficients for all nutrients, which often happens when variability is more related to systematic errors of under/overestimation than to energy intake [42][43][44]. Similarly, other studies have not reported that energy-adjusted estimates improved crude correlations [45][46][47]. The de-attenuated correlations were increased because of the correction for the day to day variation in intakes. ...
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Background: To date, no culture-specific food frequency questionnaires (FFQ) are available in North Africa. The aim of this study was to adapt and examine the reproducibility and validity of an FFQ or use in the Moroccan population. Methods: The European Global Asthma and Allergy Network (GA2LEN) FFQ was used to assess its applicability in Morocco. The GA2LEN FFQ is comprised of 32 food sections and 200 food items. Using scientific published literature, as well as local resources, we identified and added foods that were representative of the Moroccan diet. Translation of the FFQ into Moroccan Arabic was carried out following the World Health Organization (WHO) standard operational procedure. To test the validity and the reproducibility of the FFQ, 105 healthy adults working at Hassan II University Hospital Center of Fez were invited to answer the adapted FFQ in two occasions, 1 month apart, and to complete three 24-h dietary recall questionnaires during this period. Pearson correlation, and Bland-Altman plots were used to assess validity of nutrient intakes. The reproducibility between nutrient intakes as reported from the first and second FFQ were calculated using intra-class correlation coefficient (ICC). All nutrients were log-transformed to improve normality and were adjusted using the residual method. Results: The adapted FFQ was comprised of 255 items that included traditional Moroccan foods. Eighty-seven adults (mean age 27.3 ± 5.7 years) completed all the questionnaires. For energy and nutrients, the intakes reported in the FFQ1 were higher than the mean intakes reported by the 24-h recall questionnaires. The Pearson correlation coefficients between the first FFQ and the mean of three 24-h recall questionnaires were statistically significant. For validity, de-attenuated correlations were all positive, statistically significant and ranging from 0.24 (fiber) to 0.93 (total MUFA). For reproducibility, the ICCs were statistically significant and ranged between 0.69 for fat and 0.84 for Vitamin A. Conclusion: This adapted FFQ is an acceptable tool to assess usual dietary intake in Moroccan adults. Given its representativeness of local food intake, it can be used as an instrument to investigate the role of diet on health and disease outcomes.
... Energy-adjustment decreased correlation coefficients for all nutrients, which often happens when variability is more related to systematic errors of under/overestimation than to energy intake [42][43][44]. Similarly, other studies have not reported that energy-adjusted estimates improved crude correlations [45][46][47]. The de-attenuated correlations were increased because of the correction for the day to day variation in intakes. ...
... In this study, participants underwent questionnaire interviews and anthropometric measurements by well-trained nurses under a standardized protocol. Food-frequency questionnaire [13] was used to collect the information on dietary nutrition in recent one year and a variety of food, energy and nutrient intake of each participant were calculated to converted into a man-days per standard volume. ...
Article
The aim of study was to examine the relationship between the dietary nutrition and the prevalence and risk of renal damage in patients with metabolic syndrome. 260 patients with metabolic syndrome and chronic renal disease meeting criterion were recruited in this cross-sectional study. Metabolic syndrome was defined according to NCEP-ATPIII guidelines. Food-frequency questionnaire was performed to collect the information on dietary nutrition. Anthropometric measurements, including body weight, height and waist circumference were collected. Blood pressure, triglyceride, cholesterol, high density lipoprotein-cholesterol and fasting plasma glucose, renal function and 24-hour urine protein were measured. The correlations between GFR and actual nutrient intakes of participants were examined. The actual intakes of energy, carbohydrates, protein, fat and cholesterol in participate were all significantly higher than recommended nutrient intakes/adequate intakes of Chinese Dietary Reference Intakes. GFR was significantly inversely correlated with energy, protein intake, cholesterol intake, carbohydrates intake, sodium intake, calcium intake and actual protein/energy ratio. Logistic regression analyses showed that actual protein intakes/recommended protein intakes (APIs/RPIs) were significant independent predictors of GFR < 60 ml/min•1.73 m(2). Dietary nutrition is closely correlated with kidney damage in patients with metabolic syndrome. High protein intakes may be one of the risk factors of renal damage.
... Although our correlations for vitamin A in women (0.38) and carotene in men (0.28) were low, they were significant with p-value <0.05, suggesting reasonably good agreement between the two instruments. Other studies have also reported poor correlations for micronutrients [6,44,45], including vitamin A and carotene. ...
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Background The Food- Frequency Questionnaire (FFQ) is a dietary assessment tool frequently used in large-scale nutritional epidemiology studies. The goal of the present study is to validate a self-administered version of the Hawaii FFQ modified for use in the general adult population of Newfoundland and Labrador (NL). Methods Over a one year period, 195 randomly selected adults completed four 24-hour dietary recalls (24-HDRs) by telephone and one subsequent self-administered FFQ. Estimates of energy and nutrients derived from the 24-HDRs and FFQs were compared (protein, carbohydrate, fibre, fat, vitamin A, carotene, vitamin D, and calcium). Data were analyzed using the Pearson’s correlation coefficients, cross-classification method, and Bland–Altman plots. Results The mean nutrient intake values of the 24-HDRs were lower than those of the FFQs, except for protein in men. Sex and energy-adjusted de-attenuated Pearson correlation coefficients for each nutrient varied from 0.13 to 0.61. Except for protein in men, all correlations were statistically significant with p < 0.05. Cross-classification analysis revealed that on average, 74% women and 78% men were classified in the same or adjacent quartile of nutrient intake when comparing data from the FFQ and 24-HDRs. Bland–Altman plots showed no serious systematic bias between the administration of the two instruments over the range of mean intakes. Conclusion This 169-item FFQ developed specifically for the adult NL population had moderate relative validity and therefore can be used in studies to assess food consumption in the general adult population of NL. This tool can be used to classify individual energy and nutrient intakes into quartiles, which is useful in examining relationships between diet and chronic disease.
... The absolute nutrient intakes calculated from the FFQ were significantly higher than those calculated from the 24 HR for most nutrients, which is consistent with previous studies [13,17,19,21,22]. With respect to the FFQ, study subjects may respond more than once for the foods in mixed dishes. ...
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The objectives of this study were to develop a food-frequency questionnaire (FFQ) for Vietnamese female immigrants in Korea and to evaluate the validity of the FFQ. A total of 80 food items were selected in developing the FFQ according to consumption frequency, the contribution of energy and other nutrients, and the cooking methods based on one-day 24 hour recall (24HR) from 918 Vietnamese female immigrants between November 2006 and November 2007. The FFQ was validated by comparison with 24HR of 425 Vietnamese female immigrants between November 2008 and August 2009. The absolute nutrient intake calculated from the FFQ was higher than that estimated by 24HR for most nutrients. The correlation coefficients between 24HR and FFQ ranged from 0.10 (vitamin C) - 0.36 (energy) for crude intake, 0.05 (vitamin E) - 0.32 (calcium) for per 1000 kcal, and 0.08 (zinc) - 0.34 (calcium) for energy-adjusted, respectively. More than 70% of subjects were classified into the same or adjacent agreement groups for nutrients other than fiber, sodium, vitamin A, vitamin C, and vitamin E, while less than 10% of subjects were classified into complete disagreement groups. We conclude that the FFQ appears to be an acceptable tool for estimating nutrient intake and dietary patterns of Vietnamese female immigrants in Korea. Future studies to validate the FFQ using various biomarkers or other dietary assessment methods are needed.
Article
Aims and objectives: To develop and psychometrically test a food frequency questionnaire for adults at risk of coronary heart disease (Cardio-FFQ). Background: Comprehensive dietary assessment is critical for the prevention of cardiovascular disease, but appropriate instruments to perform this work are lacking. Design: A sequential mixed-methods study followed the COREQ and STROBE guidelines. Methods: This study was conducted between April 2016 and November 2017. It started with dietary history interviews (Phase 1) to identify candidate food items of the Cardio-FFQ, which validity and reliability were assessed (Phase 2) through expert consultation and four seasonal measurements, including test and retest with a 2-week gap every season. Physical activity and blood glucose and lipids were assessed seasonally, while another FFQ was administered during the fourth measurement. Content analysis was used to analyse verbatim interview transcripts, while descriptive and inferential analyses were used to simplify the Cardio-FFQ and examine its psychometric properties. Results: Phase I involved 34 participants during their first onset of acute coronary syndrome and generated 176 candidate food items (consumed by at least three participants) under 12 food categories. These food items were simplified to form the 133-item Cardio-FFQ after discarding items with trivial contributions to food commonalities or between-person variance. Further analysis showed that the simplified questionnaire had satisfactory content validity, concurrent validity, convergent validity, predictive validity, known-group validity and test-retest reliability. Conclusion: The 133-item Cardio-FFQ is a valid and reliable tool for a comprehensive dietary assessment appropriate for adults at risk of coronary heart disease. Relevance to clinical practice: Nurses may use the Cardio-FFQ to conduct a dietary assessment to better support people to commit to healthy diets, aiming to reduce the risk of coronary heart disease.
Article
Aim: To determine the relative validity of a 2-day 24-hour dietary recall (HR) designed to assess energy and nutrient intake among Chinese adults compared with a 2-day weighed dietary record (WD). Methods: Data were obtained from an ongoing population-based, prospective cohort study of adults aged 18-65 years in South China. A total of 41 adults completing a HR and a WD within 14 days were included in the present analysis. Estimations of individual mean differences, Spearman's correlation coefficients, cross-classifications and Bland-Altman plots were used to assess the agreement between the intakes of energy and 18 nutrients obtained from the HR and the WD. Results: With the exception of total fat, saturated fatty acids, thiamine, potassium and magnesium, the energy and nutrient intakes between the HR and WD showed no significant differences. All dietary intakes that were evaluated by the HR were correlated significantly with the dietary intake from the WD (de-attenuated correlation coefficients ranged from 0.10 to 0.87). The proportion of participants classified into quartiles correctly ranged from 61% for tocopherol intake to 90% for energy intake. The weighted k values ranking the participants ranged from 0.11 for tocopherol intake to 0.41 for the intakes of energy and calcium. The Bland-Altman plots showed moderate/good agreement among all the dietary intakes that were estimated from the HR and WD, except for total fat. Conclusions: This study suggests that an HR could be a valid tool for estimating the energy and nutrient intakes among adults in South China at the group level.
Article
The aim of this study was to investigate the relationships among Helicobacter pylori, dietary factors, and the risk of noncardia gastric cancer in a hospital-based case-control study in China. A case-control study of noncardia gastric cancer was performed at 3 hospitals in Xi'an, China, between September 2008 and July 2010. Participants were 257 men and women with histologically diagnosed primary noncardia gastric cancer and 514 sex- and age-matched (± 5 years) control subjects selected from the communities where the cases were living when diagnosed. A questionnaire was used to obtain information regarding potential risk factors, including diet, and blood samples were obtained to examine H pylori infection status. Positive H pylori status (odds ratio [OR], 3.2; 95% confidence interval [CI], 0.8-5.9) and high consumption of pickled foods (OR, 27.1; 95%, 8.7-79.1) appeared to increase the risk of noncardia gastric cancer, whereas high consumption of vegetables (OR, 0.3; 95% CI, 0.1-0.89), fruits (OR, 0.2; 95% CI, 0.09-0.81), and soya products (OR, 0.04; 95% CI, 0.01-0.3) appeared to decrease the risk. Consumption of meat, cereals, tubers, eggs, oils, nuts, fish, fresh fruit, and red meat was not clearly associated with risk. Effect modification was observed, such that a relatively high consumption of fruit and vegetables appeared to attenuate the association of H pylori with risk of noncardia gastric cancer (p < 0.05). Our data suggest that noncardia gastric cancer is highly preventable through modifications in dietary habits. Given the prevalence of H pylori infection worldwide, information regarding potential interaction between H pylori and lifestyle factors in gastric cancer development, including the dietary factors examined in our study, may prove valuable in future efforts at prevention.
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The authors examined the validity of a self-administered 180-item food frequency questionnaire in 125 Norwegian men aged 20–55 years who filled in the questionnaire and completed 14-day weighed records in fall 1995 to winter 1995/6. Spearman correlation coefficients between the two measurements ranged from 0.42 for percent of energy from fat to 0.66 for sugar intake (median r = 0.51). On average, 39% of the men were classified in the same quartile with the two methods, and 3% in the opposite quartile. Correlation coefficients between intake of fatty acids estimated from the questionnaire and the relative amounts of fatty acids in adipose tissue were: linoleic acid (18:2, n-6), r = 0.38; alpha-linolenic acid (18:3, n-3), r = 0.42; eicosapentaenoic acid (20:5, n-3), r = 0.52; and docosahexaenoic acid (22:6, n-3), r = 0.49. The correlations for these fatty acids between the total serum lipids and the diet were 0.16, 0.28, 0.51 and 0.52, respectively. The data suggest that very-long-chain n-3 fatty acids in adipose tissue and total serum lipids reflect the dietary intake of very-long-chain n-3 fatty acids to the same degree. No associations were observed between intake of alpha-tocopherol and concentration in adipose tissue and serum. Am J Epidemiol 1999;150: 75–87.
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Diet validation research was conducted to compare the respondents' reporting of dietary intake in a food frequency questionnaire (FFQ) with intake reported in food recalls. Because the population received annual salary increments that could modify food intake, diet validation studies (DVSs) were conducted during two time intervals. A 99-item FFQ was administered by an interviewer twice in a 1-year interval, and responses to each FFQ item were compared with 28 days of interviewer-administered food recalls that were collected in four 1-week intervals during each season of 1992/93. The second validation study in 1995/96 had a similar design to the earlier one. A prospective cohort study of lung cancer among tin miners in China was initiated in 1992, with dietary and other risk factors updated annually. Among a cohort of high risk tin miners for lung cancer, two different samples (n = 141 in 1992/93, and n = 113 in 1995/96) for each diet validation study were randomly selected from four mine units, that were representative of all worker units. Miners reported a significantly higher average frequency of intake of foods in the food recalls than the FFQ, with few exceptions. Deattenuated Pearson correlation coefficients of the frequency of food intake between the FFQ and food recalls were in the range of -0.40 to 0.72 in both studies, with higher positive correlations for beverages and cereal staples than for animal protein sources, vegetables, fruits and legumes. The percentage of individuals with exact agreement in the extreme quartiles of intake in the food recalls and FFQ ranged from 0 to 100% in both studies. Among Chinese miners, the range in correlations between the food recalls and the FFQ were due to: (i) market availability of foods during the food recall weeks compared to their annual reported intake in the FFQ; (ii) cultural perception of time; and (iii) differences in how the intake of mixed dishes and their multi-ingredient foods were reported in the recalls vs. the FFQ. The range in the percentage of agreement in the same quartiles and the changes in food intake over time may have implications for the analysis of the diet-disease relationship in this cohort.
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Validation studies of dietary instruments developed for epidemiological studies have typically used some form of diet record as the standard for comparison. Recent work suggests that comparison with diet record may overestimate the ability of the epidemiological instrument to measure habitual dietary intake, due to lack of independence of the measurement errors. The degree of regression dilution in estimating diet-disease association may therefore have been correspondingly underestimated. Use of biochemical measures of intake may mitigate the problem. In this paper, we report on the use of urinary measures of intakes of nitrogen, potassium and sodium to compare the performance of a semi-quantitative food frequency questionnaire (FFQ) and a 7-day diet diary (7DD) to estimate average intake of these nutrients over one year. In all, 179 individuals were asked to complete an FFQ and a 7DD on two occasions separated by approximately 12 months. The individuals were also asked to provide 24-hour urine samples on six occasions over a 6-9-month period, covering the time at which the record FFQ and 7DD were completed. The urine was assayed for nitrogen, potassium and sodium. The protocol was completed by 123 individuals. The data from these individuals were analysed to estimate the covariance structure of the measurement errors of the FFQ, the 7DD and a single 24-hour urine measurement, and to estimate the degree of regression dilution associated with the FFQ and 7DD. The results demonstrated that: (1) the error variances for each of the three nutrients was more than twice as great with the FFQ than the 7DD; (2) there was substantial correlation (0.46-0.58) between the error of both the FFQ and the 7DD completed on different occasions; (3) there was moderate correlation (0.24- 0.29) between the error in the FFQ and the error in the 7DD for each nutrient; (4) the correlation between errors in different nutrients was higher for the FFQ (0.77-0.80) than for the 7DD (0.52-0.70). The regression dilution with the FFQ is considerably greater than with the 7DD and also, for the nutrients considered, greater than would be inferred if validation studies were based solely on record or diary type instruments.
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An interviewer-administered quantitative food-frequency questionnaire (FFQ) was developed to determine the energy and nutrient intakes of adult Jamaicans of African origin as part of a study of the epidemiology of diabetes and hypertension. Reproducibility of the questionnaire was investigated in 123 participants aged 25-74 years. The relative validity of the FFQ was assessed against twelve 24-hour recalls administered over 12 months in 73 of the participants. In addition, energy intakes (EI) were compared with estimated basal metabolic rates (BMR). Reproducibility correlation coefficients (Pearson and intraclass) varied between 0.42 for retinol and 0.71 for carbohydrate, with most values falling between 0.50 and 0.60. When compared with repeated 24-hour recalls, the FFQ estimated slightly higher energy (mean 6%) and macronutrient intakes (mean 2-14%), and was within 5% when expressed as a percentage of energy intake. Micronutrients were higher by 1.19 (calcium) to 1.61 times (vitamin C). Unadjusted correlations between the FFQ and the reference method ranged from 0.20 for beta-carotene to 0.86 for alcohol. Cross-classification of nutrients into quartiles showed that 46-48% of participants in the lowest and highest quartiles were jointly classified by both methods. Misclassifications were low for most nutrients with one or two persons misclassified at the extreme quartiles. EI/BMR ratios suggested light to moderate activity levels appropriate for an urban population in a developing country. The FFQ showed reasonable reproducibility and validity and is suitable for estimating the habitual intakes of energy and macronutrients, but was poor for some micronutrients (retinol and beta-carotene).
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The purpose of the study was to assess the validity of a 52-item semi-quantitative food-frequency questionnaire (FFQ) by comparing it with multiple 24-hour dietary recalls. Three non-consecutive 24-hour dietary recalls and one FFQ were administered over a one-month period. Four communities of El Progreso, Guatemala. Seventy-three individuals aged 22-55 years. : Intakes of energy and other nutrients as measured by the FFQ were higher than intakes measured by 24-hour recalls. Energy was overestimated by 361 kcal, and nutrient overestimates were particularly great for vitamin C and iron. Pearson correlation coefficients for crude energy and nutrients intakes ranged from 0.64 for energy to 0.12 for vitamin C. Exact agreement for both methods (measured by the concordance correlation coefficient) ranged from 0.59 (fat) to 0.06 (vitamin C). Pearson correlation coefficients for energy-adjusted nutrients ranged from 0.59 (carbohydrates) to 0.11 (thiamin). Pearson correlation coefficients for the proportion of total energy derived from specific foods ranged from 0.59 (tortillas) to 0.01 (sugared beverages). Cross-classification of quartiles of crude nutrient intakes for both methods indicated that <11% were grossly misclassified; after adjusting for energy intake, <13% were grossly misclassified. This FFQ provides good measures of energy and macronutrient intakes and a reasonably reliable measure of micronutrient intake, indicating its suitability for comparing exposures within a study population in reference to heath-related endpoints. Our results highlight the need to adapt any FFQ to specific cultural needs - in this case, the Guatemalan 'core foods' (tortilla, bread and beans), for which inter-individual variability in intake is high.
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To evaluate the validity and reliability of the food frequency questionnaire (FFQ) used in the Shanghai Women's Health Study (SWHS), 200 SWHS participants were recruited for a dietary calibration study. Study participants completed an FFQ at baseline and 24-h dietary recalls (24-HDR) twice per month consecutively for 12 months. At the end of the study, a second FFQ was administered. Of the 200 study participants, 196 completed 24 or more days of 24-h dietary recalls, 191 completed two FFQs from whom the results of this report were based. The FFQ included the foods that accounted for 86% of the foods recorded in the 24-HDR surveys. Validity of the FFQ was evaluated by comparing intake levels of major nutrients and foods obtained from the second FFQ with those derived from the multiple 24-HDR. The median intake for major nutrients, rice, poultry and meat derived from the second FFQ and the 24-HDR was similar, with the differences ranging from 1.3 to 12.1%. The FFQ tended to overestimate the intake level of total vegetables and total fruits, and the differences were explained mainly by over-reporting seasonal vegetables and fruits consumption in the FFQ. Nutrient and food intake assessed by the FFQ and the multiple 24-HDR correlated very well, with the correlation coefficients being 0.59-0.66 for macronutrients, 0.41-0.59 for micronutrients, and 0.41-0.66 for major food groups. The reliability of the FFQ was assessed by comparing the correlation and median intake of nutrients and food groups obtained from the two FFQs that were administered approximately 2 y apart. The median intake levels for selected nutrients and food groups derived from the two FFQs were similar with differences below 10%. At the individual level, the intake levels of these dietary variables obtained from two FFQs also correlated well. When nutrient and food group intakes were categorized into quartiles, FFQ and 24-HDR produced exact agreement rates between 33 and 50%. Misclassification to adjacent quartile was common, ranging from 34-48%, while misclassification to an extreme quartile was rare (1-6%). These data indicate that the SWHS FFQ can reliably and accurately measure usual intake of major nutrients and food groups among women in Shanghai.
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To evaluate validity and reliability of the food-frequency questionnaire (FFQ) developed for the Korean Genome Epidemiologic Study (KoGES). FFQ was administered twice at 1-year interval (first FFQ (FFQ1) at the beginning and second FFQ (FFQ2) at the end of the study) and diet records (DRs) were collected for 3 days during each of the four seasons from December 2002 to May 2004 for those who attended the health examination center. At the end of the study period, we collected the 12-day DRs of 124 participants. The nutrient intakes from the DRs were compared with both FFQ1 and FFQ2. The intakes of energy and some nutrients estimated from FFQ1 and FFQ2 were different from those assessed by the DRs. Especially, the consumption of carbohydrates was higher in FFQ1 and FFQ2 than in the DRs. The de-attenuated, age, sex and energy intake adjusted correlation coefficients between the FFQ2 and the 12-day DRs in Korean population ranged between 0.23 (Vitamin A) and 0.64 (carbohydrate). The median for all nutrients was 0.39. The correlations were similar when we compared nutrient densities of both methods. Joint classification of calorie-adjusted nutrient intakes assessed by FFQ2 and 12-day DRs by quartile ranged from 25.8% (vitamin A) to 39.5% (carbohydrate, iron) for exact concordance. Except vitamin A, the proportion of subjects classified into distant quartile was less than 7% in all nutrients. The median of correlations between the two FFQs 1 year apart were 0.45 for all nutrient intakes and 0.39 for nutrient densities. We conclude that the FFQ we have developed appears to be an acceptable tool for assessing the nutrient intakes in this population. Further studies for calibration of the FFQ collected from multicenters participating in the KoGES are needed. This study was supported by the budget of the National Genome Research Institute, Korea National Institute of Health (2002-347-6111-221).
Article
Objectives: To evaluate the reproducibility of, and to compare and calibrate, diet measures by the Northern Sweden 84-item food-frequency questionnaire (FFQ) with measures from 24-hour diet recalls (24-HDR). Design: Randomly selected respondents from the EPIC (diet-cancer) and MONICA (diet-cardiovascular disease) study cohort in Northern Sweden were invited to answer the FFQ twice over a one-year interval (FFQ1 and FFQ2), and to complete ten 24-hour recalls (reference method) in the months between. Plasma beta-carotene concentrations were determined from a subset of 47 participants. Setting: Västerbotten and Norrbotten, Northern Sweden. Participants: Ninety-six men and 99 women, who completed the study. Results: The reproducibility of the FFQ was high in terms of both mean energy and nutrient intakes and relative ranking of participants by intake levels (median Pearson correlation of 0.68). Moderately higher food intake frequencies were recorded by FFQ1 compared with 24-hour recalls for dairy products, bread/cereals, vegetables, fruits and potato/rice/pasta, whereas meat, fish, sweet snacks and alcoholic beverage intakes were lower. The median Spearman coefficient of correlation between FFQ1 and the average of ten 24-HDR measurements was 0.50. Daily energy and nutrient intakes were similar for FFQ1 and 24-HDR measurements, except for fibre, vitamin C, beta-carotene and retinol (FFQ1>24-HDR) and sucrose and cholesterol Pearson coefficients of correlation between FFQ1 and 24-HDR corrected for attenuation due to residual day-to-day variation in the 24-HDR measurements ranged from 0.36 to 0.79 (median 0.54). Adjustment for energy had only very moderate effects on the correlation estimates. Calibration coefficients estimated by linear regression of the 24-HDR on the FFQ1 measurements varied between 0.30 and 0.59 for all nutrients except alcohol, which had calibration coefficients close to 1.0. These low calibration coefficients indicate that relative risk estimates corresponding to an absolute difference in dietary intake levels measured by the FFQ will generally be biased towards 1.0. Plasma beta-carotene levels had a Pearson coefficient of correlation of 0.47 with the 24-HDR measurements, and of 0.23 with FFQ1 measurements. Conclusions: The Northern Sweden FFQ measurements have good reproducibility and an estimated level of validity similar to that of FFQ measurements in other prospective cohort studies. The results from this study will form the basis for the correction of attenuation and regression dilution biases in relative risk estimates, in future studies relating FFQ measurements to disease outcomes.
Chapter
Total energy intake deserves special consideration in nutritional epidemiology for three reasons: firstly, the level of energy intake may be a primary determinant of disease; secondly, individual differences in total energy intake produce variation in intake of specific nutrients unrelated to dietary composition because the consumption of most nutrients is positively correlated with total energy intake; and, thirdly, when energy intake is associated with risk of disease but is not a direct cause, associations with specific nutrients may be distorted (confounded) by total energy intake. Before examining these three issues in detail, this chapter discusses the physiologic aspects of energy utilization and the determinants of variation in energy intake in epidemiologic studies.
Article
Background Validation studies of dietary instruments developed for epidemiological studies have typically used some form of diet record as the standard for comparison. Recent work suggests that comparison with diet record may overestimate the ability of the epidemiological instrument to measure habitual dietary intake, due to lack of independence of the measurement errors. The degree of regression dilution in estimating diet-disease association may therefore have been correspondingly underestimated. Use of biochemical measures of intake may mitigate the problem. In this paper, we report on the use of urinary measures of intakes of nitrogen, potassium and sodium to compare the performance of a semi-quantitative food frequency questionnaire (FFQ) and a 7-day diet diary (7DD) to estimate average intake of these nutrients over one year. Methods In all, 179 individuals were asked to complete an FFQ and a 7DD on two occasions separated by approximately 12 months. The individuals were also asked to provide 24-hour urine samples on six occasions over a 6-9-month period, covering the time at which the record FFQ and 7DD were completed. The urine was assayed for nitrogen, potassium and sodium. The protocol was completed by 123 individuals. The data from these individuals were analysed to estimate the covariance structure of the measurement errors of the FFQ, the 7DD and a single 24-hour urine measurement, and to estimate the degree of regression dilution associated with the FFQ and 7DD. Results The results demonstrated that: (I) the error variances for each of the three nutrients was more than twice as great with the FFQ than the 7DD; (2) there was substantial correlation (0.46-0.58) between the error of both the FFQ and the 7DD completed on different occasions; (3) there was moderate correlation (0.24-0.29) between the error in the FFQ and the error in the 7DD for each nutrient; (4) the correlation between errors in different nutrients was higher for the FFQ (0.77-0.80) than for the 7DD (0.52-0.70). Conclusions The regression dilution with the FFQ is considerably greater than with the 7DD and also, for the nutrients considered, greater than would be inferred if validation studies were based solely on record or diary type instruments.
Article
Numerous factors affect the reproducibility and validity of dietary assessment questionnaires. Although the respondents' abilities to respond accurately are most frequently discussed as the cause of apparently poor reproducibility and validity, many other factors are as important and perhaps more important. Most of these other factors are under the control of the investigator, and thus are amenable to improvement. Factors which may affect reproducibility included the degree of variability permitted by the instrument, the error-proneness of the response format, quality control of coding and keying and real dietary change in the time between the two administrations of the questionnaire. Factors affecting real or apparent validity include respondent characteristics, questionnaire design and quantification, quality control, and the adequacy of the reference data. The implications of inadequate reference data are illustrated and discussed.
Article
In prospective studies of diet it is often necessary to know for how many days subjects should record food consumption in order to be able to rank subjects correctly according to their nutrient intakes. Data from six studies--of toddlers, families, schoolchildren, dietitians, pregnant women, and elderly subjects--were analyzed to estimate the number of recording days necessary for energy, 28 nutrients, and the ratio of polyunsaturated to saturated fatty acids (P:S). The most striking finding is that 7 d of diet record do not rank subjects with the degree of accuracy commonly assumed. For some nutrients, such as iron, zinc, nicotinic acid, and pyridoxine, it may be desirable to record diet over a number of short, separate periods to achieve the number of days required. For others, such as copper, retinol, carotene, vitamin B-12, polyunsaturated fatty acids, P:S, and alcohol, alternative methods of assessment based on dietary histories or questionnaires may be more appropriate.
Article
It is well known that random measurement error can attenuate the correlation coefficient between two variables. One possible solution to this problem is to estimate the correlation coefficient based on an average of a large number of replicates for each individual. As an alternative, several authors have proposed an unattenuated (or corrected) correlation coefficient which is an estimate of the true correlation between two variables after removing the effect of random measurement error. In this paper, the authors obtain an estimate of the standard error for the corrected correlation coefficient and an associated 100% x (1-alpha) confidence interval. The standard error takes into account the variability of the observed correlation coefficient as well as the estimated intraclass correlation coefficient between replicates for one or both variables. The standard error is useful in hypothesis testing for comparisons of correlation coefficients based on data with different degrees of random error. In addition, the standard error can be used to evaluate the relative efficiency of different study designs. Specifically, an investigator often has the option of obtaining either a few replicates on a large number of individuals, or many replicates on a small number of individuals. If one establishes the criterion of minimizing the standard error of the corrected coefficient while fixing the total number of measurements obtained, in almost all instances it is optimal to obtain no more than five replicates per individual. If the intraclass correlation is greater than or equal to 0.5, it is usually optimal to obtain no more than two replicates per individual.
Article
The relation between diet and endometrial cancer was examined in a population-based case-control study conducted in Shanghai, People's Republic of China, between 1988 and 1990, involving interviews with 268 cases and 268 controls aged 18-74 years. The subjects' usual dietary intake of 63 major foods during the previous 10 years (disregarding any recent changes) was measured by means of a structured quantitative food questionnaire. Although women in the highest quartile of total caloric intake had a 2.1-fold increased risk of endometrial cancer, risk varied according to the source of calories. The highest quartiles of caloric intake from fat and protein were associated with odds ratios of 3.9 and 3.1, respectively, while calories from carbohydrates, the major contributor of total calories in this population, were not related to risk. The association of fat and protein with endometrial cancer risk was confined to foods of animal origin in the diet. After adjustment for age, body mass index (weight (kg)/height (m)2), and number of pregnancies, odds ratios were 3.5 (95% confidence interval (CI) 2.0-6.0) and 3.0 (95% CI 1.7-5.1) for women in the highest quartiles of intake of animal fat and animal protein, respectively. Food group analyses showed a similar pattern, with high consumption of meat, eggs, and fresh fish being associated with elevated risks. After adjustment for total calories, no significant association of risk was found with intake of vegetables or dark green/yellow vegetables, or with estimated carotene intake, although fruit and allium vegetables were associated with some reduction in risk. These results suggest that diets rich in animal fat and animal protein may play an important role in the etiology of endometrial cancer.
Article
To evaluate the reproducibility of, and to compare and calibrate, diet measures by the Northern Sweden 84-item food-frequency questionnaire (FFQ) with measures from 24-hour diet recalls (24-HDR). Randomly selected respondents from the EPIC (diet-cancer) and MONICA (diet-cardiovascular disease) study cohort in Northern Sweden were invited to answer the FFQ twice over a one-year interval (FFQ1 and FFQ2), and to complete ten 24-hour recalls (reference method) in the months between. Plasma beta-carotene concentrations were determined from a subset of 47 participants. Västerbotten and Norrbotten, Northern Sweden. Ninety-six men and 99 women, who completed the study. The reproducibility of the FFQ was high in terms of both mean energy and nutrient intakes and relative ranking of participants by intake levels (median Pearson correlation of 0.68). Moderately higher food intake frequencies were recorded by FFQ1 compared with 24-hour recalls for dairy products, bread/cereals, vegetables, fruits and potato/rice/pasta, whereas meat, fish, sweet snacks and alcoholic beverage intakes were lower. The median Spearman coefficient of correlation between FFQ1 and the average of ten 24-HDR measurements was 0.50. Daily energy and nutrient intakes were similar for FFQ1 and 24-HDR measurements, except for fibre, vitamin C, beta-carotene and retinol (FFQ1>24-HDR) and sucrose and cholesterol Pearson coefficients of correlation between FFQ1 and 24-HDR corrected for attenuation due to residual day-to-day variation in the 24-HDR measurements ranged from 0.36 to 0.79 (median 0.54). Adjustment for energy had only very moderate effects on the correlation estimates. Calibration coefficients estimated by linear regression of the 24-HDR on the FFQ1 measurements varied between 0.30 and 0.59 for all nutrients except alcohol, which had calibration coefficients close to 1.0. These low calibration coefficients indicate that relative risk estimates corresponding to an absolute difference in dietary intake levels measured by the FFQ will generally be biased towards 1.0. Plasma beta-carotene levels had a Pearson coefficient of correlation of 0.47 with the 24-HDR measurements, and of 0.23 with FFQ1 measurements. The Northern Sweden FFQ measurements have good reproducibility and an estimated level of validity similar to that of FFQ measurements in other prospective cohort studies. The results from this study will form the basis for the correction of attenuation and regression dilution biases in relative risk estimates, in future studies relating FFQ measurements to disease outcomes.
Article
Methods to evaluate food consumption still need improvement. A study was conducted to verify the reproducibility and validity of a food frequency questionnaire (FFQ) among overweight adults. The study was carried out in a private university in São Paulo, Brazil. The study sample consisted of 146 individuals of both sex with body mass index =25 kg/m2 and age between 18 and 60 years old. For reproducibility the FFQ was applied by trained interviewers at two different instances with a mean interval time of 47 days. For validity, data collected from the FFQ were compared with those obtained from the average of 3 different daily records of a 24-hour dietary recall (mean interval time: 15 days). Validity and reproducibility of data on calories and macronutrients consumption was assessed using pondered kappa statistics and intraclass correlation coefficient. A higher variability in the reporting of regular food consumption was seen among obese than overweight individuals. Concerning reproducibility, kappa statistical values varied from 0.23 (carbohydrates and fats) to 0.40 (calories), and intraclass correlation coefficients ranged from 0.28 (protein) to 0.54 (total calories). For FFQ validity, the highest kappa value was 0.25 (calories), and the intraclass correlation coefficient was 0.21 (protein). Food consumption reports of overweight individuals tend to be underestimated. Despite its limitations, FFQ could be used in epidemiological studies to assess the regular food consumption of overweight individuals.
Article
To validate a self-administered 20-item short questionnaire (SQ) for classifying individuals according to their intake of total fat, saturated (SFA), monounsaturated (MUFA), and polyunsaturated fatty acids (PUFA), as well as cholesterol. The SQ was sent to a randomly selected subsample of 300 participants of the European Prospective Investigation into Cancer and Nutrition (EPIC) in Heidelberg. The SQ was sent back by 244 participants (52.5% women, 47.5% men). Intake of total fat, SFA, MUFA, PUFA, and cholesterol was calculated from a 148-item food frequency questionnaire (FFQ). The intake was compared with the scores computed from the SQ. Spearman's correlation coefficient between the intake estimated from the FFQ and the score from the SQ ranged from r = 0.29 (PUFA) to r = 0.56 (cholesterol). When the participants were assigned to quartiles of intake according to both methods 29-42% were classified into the same quartile, 1-7% of the participants were grossly misclassified. The SQ demonstrated a good validity with respect to SFA and cholesterol and an acceptable validity with respect to total fat and MUFA, while the results are less good for PUFA. The SQ can be used to classify persons according to their intake into categories of intake.
Article
We examined the reproducibility of a self-administered semiquantitative food frequency questionnaire (FFQ) used in the 5-year follow-up survey for the Japan Public Health Center-based prospective Study on cancer and cardiovascular diseases (JPHC Study) to estimate nutrient and food intake by using repeated FFQs at a 1-year interval in 101 men and 108 women. Between energy and each of 32 nutrients, the correlation coefficients in crude values varied from 0.41 for vitamin B12 to 0.83 for alcohol (median=0.59) in men and 0.52 for alpha-carotene to 0.77 for iron (median=0.67) in women. In 21 food groups, it varied from 0.42 for seasonings and spices to 0.80 for pickled vegetables (median=0.61) in men and 0.45 for seasonings and spices and 0.74 for pulses, milks, and pickled vegetables (median=0.63) in women. The correlation coefficients for the energy-adjusted values (medians were 0.49 and 0.50 for nutrients and 0.50 and 0.49 for food groups in men and women, respectively) were somewhat lower than for the crude values. The difference in mean intakes between the two FFQs was less than 10% in most of the nutrient and food groups. The results suggest that the reproducibility of the FFQ used for the JPHC study was moderate to high in most of the nutrient and food groups.
Article
Pooled analyses of cohort studies show no relation between fat intake and breast-cancer risk. However, food-frequency questionnaire (FFQ) methods used in these studies are prone to measurement error. We assessed diet with an FFQ and a detailed 7-day food diary in 13070 women between 1993 and 1997. We compared 168 breast-cancer cases incident by 2000 with four matched controls. Risk of breast cancer was associated with saturated-fat intake measured with the food diary (hazard ratio 1.22 [95% CI 1.06-1.40], p=0.005, per quintile increase in energy-adjusted fat intake), but not with saturated fat measured with the FFQ (1.10 [0.94-1.29], p=0.23). Dietary measurement error might explain the absence of a significant association between dietary fat and breast-cancer risk in cohort studies.
Article
We developed three ethnic food frequency questionnaires (FFQs) to characterize the diets of South Asian, Chinese, and European immigrants. FFQs were developed from foods reported in the diet records and recalls of 29 South Asians, 25 Chinese, and 20 Europeans participating in a pilot study from 1995-1996 in Hamilton, Ontario, Canada. The FFQ and a seven-day diet record were then administered to 342 South Asians, 317 Chinese, and 346 Europeans participating in the Study of Health Assessment and Risk in Ethnic groups (SHARE) in three Canadian centers from 1996-1998. For FFQ validation, a subset of these participants completed a second seven-day diet record and second FFQ 8 to 10 months later. The FFQ generally underestimated macronutrient and overestimated micronutrient intake compared with the records. Consumption of most macronutrients was lower among South Asians. Energy-adjusted deattenuated correlation coefficients between the records and second FFQ ranged from 0.32 to 0.73 (South Asians), 0.17 to 0.84 (Chinese), and 0.30 to 0.83 (Europeans). The FFQs generally performed well and will be used to investigate diet-disease relations in SHARE. Lower correlations for dietary fats among Chinese persons (0.17 to 0.31) may be improved with more direct questions on the FFQ regarding brand, type, and amount of oil consumed in stirfry servings.
Article
Although many validation studies of FFQ have been reported, only a few addressed the effect of inclusion of dietary supplement use on the validity of micronutrient estimates. The purpose of the present study was to assess reproducibility and validity of a self-administered FFQ, intended to measure total nutrient intake from diet and from dietary supplements, in a random population-based sample of 248 middle-aged and elderly men (40-74 y old) in central Sweden. Fourteen 24-h recall interviews were used as the reference method. Participants were telephoned about once a month for 1 y, covering every day of the week, twice in random order. Spearman correlation coefficients increased 13% (from 0.49 to 0.62), between FFQ-based micronutrient estimates and the fourteen 24-h recall interviews (reference method) when supplement use was included. Correct classification into highest quintiles was also improved by 14% (from 37 to 51%). There were no differences in mean intraclass correlation coefficients for 1-y reproducibility between total micronutrient intake and micronutrients from foods only. The increase in the validity of micronutrient estimates due to inclusion of supplements in nutrient intake assessment has important implications for sample size in epidemiologic studies. Because a dramatic increase in dietary supplement use has occurred in recent decades in many countries, the issue of including supplements in dietary assessment should be of highest priority in nutritional epidemiologic studies of chronic diseases.
Article
To examine the validity and reproducibility of a self-administered food-frequency questionnaire (FFQ) used for two cohort studies in Japan. Cross-sectional study. Two rural towns in the Miyagi Prefecture, in north-eastern Japan. Fifty-five men and 58 women. A 40-item FFQ was administered twice, 1 year apart. In the mean time, four 3-day diet records (DRs) were collected in four seasons within the year. We calculated daily consumption of total energy and 15 nutrients, 40 food items and nine food groups from the FFQs and the DRs. We computed Spearman correlation coefficients between the FFQs and the DRs. With adjustment for age, total energy and deattenuation for measurement error with the DRs, the correlation coefficients for nutrient intakes ranged from 0.25 to 0.58 in men and from 0.30 to 0.69 in women, with median of 0.43 and 0.43, respectively. Median (range) of the correlation coefficients was 0.35 (-0.30 to 0.72) in men and 0.34 (-0.06 to 0.75) in women for food items and 0.60 (-0.10 to 0.76) and 0.51 (0.28-0.70) for food groups, respectively. Median (range) of the correlation coefficients for the two FFQs administered 1 year apart was 0.49 (0.31-0.71) in men and 0.50 (0.40-0.64) in women for nutrients, 0.43 (0.14-0.76) and 0.45 (0.06-0.74) respectively for food items, and 0.50 (0.30-0.70) and 0.57 (0.39-0.66) respectively for food groups. Relatively higher agreement percentages for intakes of nutrients and food groups with high validity were obtained together with lower complete disagreement percentages. The FFQ has a high reproducibility and a reasonably good validity, and is useful in assessing the usual intakes of nutrients, foods and food groups among a rural Japanese population.
Article
(1). To determine the reliability and validity of a food-frequency questionnaire (FFQ) for use in epidemiological research in postmenopausal women; and (2). to compare the volume estimation (VE) and weight estimation (WE) method of administration of this questionnaire. An initial list of foods was derived and modified after pre-testing in 22 subjects. Test-retest reliability was assessed in 21 subjects who had repeat administrations of the questionnaire 14 days apart (FFQ1, FFQ2). The validity of the FFQ was assessed by comparing nutrient intakes with those from a 4-day food record.Setting: Chengdu, People's Republic of China. Twenty-two postmenopausal women (50-70 years) were recruited from The Second University Hospital, West China University of Medical Sciences, Chengdu and participated in the pre-test. Another 21 women (50-70 years) were randomly selected from the general population of all five districts of Chengdu and participated in the reliability and validity sub-studies. Energy, protein, carbohydrate, magnesium and sodium intakes in this sample were less than the Recommended Dietary Allowances (RDAs) for 45-70-year-old women in China. Intake of non-cooking fat was higher than the Chinese RDA. Pearson correlation coefficients and intra-class correlation coefficients (ICCs) for reliability of the VE FFQ ranged from 0.51 to 0.85 and from 0.51 to 0.81, respectively; for the WE FFQ, they ranged from 0.22 to 0.86 and from 0.21 to 0.81. Correlation coefficients and ICCs for validity of the WE FFQ ranged from 0.36 to 0.69 and from 0.34 to 0.57, respectively; corresponding values for the VE FFQ were -0.30 to 0.65 and -0.14 to 0.65. Both the VE and WE FFQs were reliable and valid except for sodium intake. The VE FFQ provided more valid estimates of nutrient intakes than did the WE FFQ.
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