Odds ratio or prevalence ratio? Their use in cross-sectional studies
ABSTRACT The most commonly used measures of association in cross-sectional studies are the odds ratio (OR) and the prevalence ratio (PR). Some cross-sectional epidemiologic studies describe their results as OR but use the definition of PR. The main aim of this study was to describe and compare different calculation methods for PR described in literature using two situations (prevalence < 20% and prevalence > 20%).
A literature search was carried out to determine the most commonly used techniques for estimating the PR. The four most frequent methods were: 1) obtaining the OR using non-conditional logistic regression but using the correct definition; 2) using Breslow-Cox regression; 3) using a generalized linear model with logarithmic transformation and binomial family, and 4) using the conversion formula from OR into PR. The models found were replicated for both situations (prevalence less than 20% and greater than 20%) using real data from the 1994 Catalan Health Interview Survey.
When prevalence was low, no substantial differences were observed in either the estimators or standard errors obtained using the four procedures. When prevalence was high, differences were found between estimators and confidence intervals although all the measures maintained statistical significance.
All the methods have advantages and disadvantages. Individual researchers should decide which technique is the most appropriate for their data and should be consistent when using an estimator and interpreting it.
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- "Statistically significant variables with a p-value <0.20 in the bivariate analysis were entered into the logistic model, starting with the variable that had the highest level of statistical significance and following in descending order. Odds ratios (OR) and confidence intervals (95%) were converted into prevalence ratios (PR) as recommended by Schiaffino et al. . The data were analyzed using SPSS 16.0 (SPSS, Inc., Chicago, IL, USA) "
ABSTRACT: Background Aesthetic alterations in the face can be self-perceived and can affect quality of life. For young people, physical attractiveness is an important factor affecting social relationships. The aim of this study was to estimate the prevalence of malocclusion, identify the most common types and test its association with oral aesthetic self-perception in 18 to 21 year-old population of male young adults. Methods A cross-sectional study was carried out involving 138 Brazilian Army soldiers. Data collection included socio demographic profile, malocclusion status through the Dental Aesthetic Index (DAI) and oral aesthetic self-perception as indicated by the Oral Aesthetic Subjective Impact Scale (OASIS). The chi-square and Fisher’s exact test were used to test for homogeneity of proportions. The stepwise multivariate logistic regression analysis was used to test for the relationship between the poorer oral aesthetic self-perception and parental and soldier’s education, per capita income, history of caries in all teeth and only on anterior teeth, dental trauma, previous orthodontic treatment and malocclusion. Results The prevalence of malocclusion was 45.6%. Incisor teeth crowding and misalignment of lower incisors were the most common types of malocclusions. A statistically significant and independent association between malocclusion and poorer oral aesthetic self-perception in the multivariate analysis was observed. Subjects with severe malocclusion conditions showed 88% higher prevalence [prevalence ratio =1.88 (95% CI, 1.30 – 2.72); p = 0.001] of poorer aesthetic self-perception comparing to those with minor malocclusion. Conclusions A high prevalence of malocclusion was observed. The young adults presenting severe malocclusion had a higher and independent prevalence of poorer oral aesthetic self-perception.BMC Oral Health 01/2013; 13(1):3. DOI:10.1186/1472-6831-13-3 · 1.15 Impact Factor
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ABSTRACT: To describe trends in fertility, fetal death rate, prematurity and low birth weight, as well as their association with advanced maternal age, in Spain from 1996 to 2005. We performed an ecological study. The association between low birth weight and prematurity with maternal age was analyzed through contingency tables. The pattern of fetal mortality rate was analyzed through direct standardization. To study the risk of late fetal mortality, adjusted by age and prematurity, a Poisson regression model was used. The rates of fertility and late fetal mortality increased in women aged more than 35 years, especially in women aged more than 45 years. The risk of late fetal mortality was 2.7 times higher in women aged 45 years and above (rate ratio, 2.7; 95%CI: 1.8-3), with an etiological fraction of exposure of 69% (95%CI: 55.2-78.6). The prevalence rate of prematurity and low birth weight was three times higher in this age group, with a prevalence rate of prematurity of 2.9 (95%CI: 2.7-3.1) and of low birth weight of 3.1 (95%CI: 2.9-3.3). The high risk found in women aged more than 45 years is explained by the increase in the proportion of pregnancies within this age group during the period analyzed. Further studies in perinatal epidemiology that analyze the impact of assisted reproduction techniques in pregnancies in older women are required, as well as a national registry of assisted reproduction techniques.Gaceta Sanitaria 22(5):396-403. · 1.25 Impact Factor
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ABSTRACT: To illustrate -for the first time with Spanish data- the usefulness of telephone-interview-based surveillance of non-communicable diseases risk factors for the purpose of drawing up public health policies. We analysed information from the Non-Communicable Disease Risk Factor Surveillance System (Sistema de Vigilancia de Factores de Riesgo asociados a Enfermedades No Transmisibles- SIVFRENT) for the period 1995-2003. This system is based on monthly telephone interviews covering a representative population sample, aged 18-64 years. 18,049 interviews were conducted for the whole period. Indicators of overweight and obesity, sedentary lifestyle, diet, tobacco and alcohol consumption, preventive practices, accidents and injuries, and road safety were calculated. The time trend was estimated using average annual prevalence ratios, obtained from generalised linear models with binomial family and logarithmic link. Among men, the changes of greatest magnitude corresponded to an increase in overweight and obesity, which registered a relative annual rise of 3.7%, and a decrease in dieting (-3%), high alcohol consumption (-6.1%) and non-use of safety belts (-4%). Among women, there was a marked increase in overweight and obesity (3.3%), cessation of smoking (3.1%) and recourse to mammograms (6.4%), and a decrease in dieting (-4.1%) and non-use of safety belts (-4.5%). Although important progress was observed in a number of indicators, such as tobacco and alcohol consumption, road safety and the undertaking of preventive practices, the situation worsened in others, i.e., fundamentally the increase in overweight and obesity.Gaceta Sanitaria 05/2005; 19(3):193-205. · 1.25 Impact Factor