Assessing the known or intended effects of a drug using non-experimental epidemiologic designs is often infeasible because of the absence of accurate data on a major confounder, the severity of the disease treated by this drug. To circumvent this problem of confounding by indication, I propose the case-time-control design, which does not require a measure of this confounder. Instead, the design uses subjects from a conventional case-control design as their own controls and thus requires that exposure be measurable at two or more points in time. I present a logistic model to estimate relative risks under this design and illustrate the method with data from a case-control study of 129 cases of fatal or near-fatal asthma and 655 controls. The exposure of interest was quantity of use of inhaled beta-agonists, drugs prescribed for the treatment of asthma. I found that the "best" estimate of relative risk for high vs low beta-agonist use using the conventional case-control approach is 3.1 [95% confidence interval (CI) = 1.8-5.4], which inherently includes the confounding effect of unmeasured severity. The corresponding estimate of drug effect using the proposed case-time-control approach is 1.2 (95% CI = 0.5-3.0), which excludes the confounding effect of unmeasured severity. This example indicates that the class of beta-agonists may not play the leading role attributed to it in the risk of fatal or near-fatal asthma, as had been previously suspected, except perhaps at excessive doses, as indicated by the dose-response analyses.
The case-time-control design is a strategy that was developed to tackle the problem of confounding by indication in the nonexperimental assessment of intended or known effects of drugs. By using subjects as their own controls, the case-time-control design, under an explicitly defined model, eliminates the biasing effect of unmeasured confounding factors in the situation where exposure varies over time. The correct application of this design is based on a specific model that contains inherent assumptions and imposes certain conditions for the approach to be valid. In a recent article, Greenland questioned the validity of the case-time-control design by presenting several "counterexamples." In this paper, we review the assumptions inherent to the validity of the case-time-control model. We show that the presumed counterexamples are not what they are claimed to be, simply because they do not conform to the logistic model explicitly underlying the case-time-control approach. These examples are shown to arise from an alternative model that includes a confounder by period interaction, a term expressly avoided in the case-time-control model. When the data from these examples are modified to satisfy the correct model, the resulting case-time-control estimates of the treatment odds ratio are exactly 2, the true treatment effect. We clarify the necessity of this assumption in the context of matching in epidemiology. We also discuss briefly the assumptions of conditional independence and carryover effects.
A cohort of 1,904 vegetarians and persons leading a health-conscious life-style in the Federal Republic of Germany was identified in 1978. After a follow-up of 11 years, mortality from all causes was reduced by one-half compared with the general population [the standardized mortality ratio (SMR) was 0.44 for men, 0.53 for women]. Among the 858 men, 111 deaths were observed, with 255 expected; among the 1,046 women, 114 deaths were observed, with 215 expected. The lowest mortality was found for cardiovascular diseases (SMR = 0.39 for men, 0.46 for women); in particular, for ischemic heart diseases, mortality was reduced to one-third of that expected. Cancer mortality was reduced by one-half in men (SMR = 0.48), but only by one-quarter in women (SMR = 0.74). The deficit in cancer deaths was mainly observed for lung cancer and gastrointestinal cancers in males and for gastrointestinal cancers in females. Deaths from diseases of the respiratory and digestive systems were also reduced by about 50%. An excess of deaths occurred only for anemia. When the strict and the moderate vegetarians were analyzed separately, the strongest differential was found for ischemic heart diseases, which were much less frequent among strict vegetarians for both sexes. Some nondietary factors, such as higher socioeconomic status, virtual absence of smoking, and lower body mass index, may also have contributed to the lower mortality of the study participants.
We assessed the impact of smoking cessation on subsequent death rates among a cohort of 51,343 men and 66,751 women in California enrolled in late 1959 in the original American Cancer Society (ACS) Cancer Prevention Study (CPS I) and followed for 38 years. We compared the age-adjusted death rate, expressed as deaths per 1,000 person-years, among all subjects who smoked cigarettes in 1959 but who had largely quit as of 1997 with the death rate among never smokers over a 38-year period. The all causes death rate for males decreased from 20.67 during 1960-1969 to 18.68 during 1960-1997 for smokers and decreased from 10.51 to 9.46 for never smokers. The lung cancer death rate for males increased from 1.558 to 1.728 for smokers and increased from 0.127 to 0.133 for never smokers. The all causes death rate for females increased from 9.54 to 10.14 for smokers and decreased from 6.95 to 6.44 for never smokers. The lung cancer death rate for females increased greatly from 0.208 to 0.806 for smokers and increased from 0.094 to 0.116 for never smokers. These results indicate there has been no important decline in either the absolute or relative death rates from all causes and lung cancer for cigarette smokers as a whole compared with never smokers in this large cohort, in spite of a substantial degree of smoking cessation. While cessation clearly reduces the mortality risk among long-term former smokers, the population impact of cessation appears to be less than currently believed.
We hypothesized that stress induced by the terrorist attacks of September 11, 2001 might shorten pregnancy. To test this hypothesis, we compared gestational duration and risk of preterm delivery among women who were pregnant on September 11 with women who had delivered before that date.
We conducted a matched cohort study among pregnant women enrolled in the Boston-based cohort study Project Viva between 1999 and 2001. Each of 606 participants, pregnant on September 11, 2001, was matched to 1 or 2 participants who delivered before that date.
Compared with women who delivered before September 11th, women who were pregnant on September 11th had mean gestation length that was 0.13 weeks longer (95% confidence interval = -0.05 to 0.30) and an odds ratio for preterm delivery before 37 weeks' gestation of 0.60 (0.36 to 0.98). Only women exposed in the first trimester had longer gestation.
Contrary to expectation, Boston-area women who were pregnant on September 11th had a lower risk of preterm delivery than women who delivered before that date. Although the interpretation of this finding is difficult, it is clear that the acute psychologic stress documented nationwide after the terrorist attacks did not increase the risk of preterm delivery in this population at some distance from the attacks.
We examined the study design features and data collection methods from 13 case-control studies of colorectal cancer and diet, which had been previously combined and analyzed, to determine whether they influenced the results obtained from a pooled analysis. We assessed the methods used in each study, estimated a quality score, and used random effects models to re-estimate the pooled odds ratio for the association between dietary fiber and colorectal cancer for these data. Key features of the methods used in each study and the quality score were examined in random effects models to determine whether the heterogeneity found between study-specific risk estimates could be explained by these variables. The odds ratio for dietary fiber and colorectal cancer was 0.46 (95% confidence interval = 0.34-0.64) for the 13 case-control studies as estimated with a random effects model. Two factors, whether the diet questionnaire had been validated before use in the case-control study and whether qualitative data on dietary habits and cooking methods had been incorporated into the nutrient estimation, explained some of the heterogeneity found between studies. Risk estimates for dietary fiber and colorectal cancer were closer to the null for the studies that had these two characteristics. Quality score did not explain any between-study heterogeneity. Random effects models, which included fixed effects covariates, explained some between-study heterogeneity in these data and would be useful for future pooled analyses.
Recently, an association was reported between prenatal and postnatal exposure to cell phones and neurobehavioral problems in children at the age of 7 years.
A birth cohort was established in Sabadell, Spain between 2004 and 2006. Mothers completed questions about cell phone use in week 32 of the pregnancy (n = 587). Neurodevelopment of their children was tested at age 14 months using the Bayley Scales of Infant Development (n = 530).
We observed only small differences in neurodevelopment scores between the offspring of cell phone users and nonusers. Those of users had higher mental development scores and lower psychomotor development scores, which may be due to unmeasured confounding. There was no trend with amount of cell phone use within users.
This study gives little evidence for an adverse effect of maternal cell phone use during pregnancy on the early neurodevelopment of offspring.
The t(14;18) translocation is a common somatic mutation in non-Hodgkin's lymphoma (NHL) that is associated with bcl-2 activation and inhibition of apoptosis. We hypothesized that some risk factors might act specifically along t(14;18)-dependent pathways, leading to stronger associations with t(14;18)-positive than t(14;18)-negative non-Hodgkin's lymphoma. Archival biopsies from 182 non-Hodgkin's lymphoma cases included in a case-control study of men in Iowa and Minnesota (the Factors Affecting Rural Men, or FARM study) were assayed for t(14;18) using polymerase chain reaction amplification; 68 (37%) were t(14;18)-positive. We estimated adjusted odds ratios (OR) and 95% confidence intervals (CI) for various agricultural risk factors and t(14;18)-positive and -negative cases of non-Hodgkin's lymphoma, based on polytomous logistic regression models fit using the expectation-maximization (EM) algorithm. T(14;18)-positive non-Hodgkin's lymphoma was associated with farming (OR 1.4, 95% CI = 0.9-2.3), dieldrin (OR 3.7, 95% CI = 1.9-7.0), toxaphene (OR 3.0, 95% CI = 1.5-6.1), lindane (OR 2.3, 95% CI = 1.3-3.9), atrazine (OR 1.7, 95% CI = 1.0-2.8), and fungicides (OR 1.8, 95% CI = 0.9-3.6), in marked contrast to null or negative associations for the same self-reported exposures and t(14;18)-negative non-Hodgkin's lymphoma. Causal relations between agricultural exposures and t(14;18)-positive non-Hodgkin's lymphoma are plausible, but associations should be confirmed in a larger study. Results suggest that non-Hodgkin's lymphoma classification based on the t(14;18) translocation is of value in etiologic research.
Persistent organic pollutants may affect the immune and respiratory systems, but available evidence is based on small study populations. We studied the association between prenatal exposure to dichlorodiphenyldichloroethylene (DDE) and polychlorinated biphenyl 153 (PCB 153) and children's respiratory health in European birth cohorts.
We included 4608 mothers and children enrolled in 10 birth cohort studies from 7 European countries. Outcomes were parent-reported bronchitis and wheeze in the first 4 years of life. For each cohort, we performed Poisson regression analyses, modeling occurrences of the outcomes on the estimates of cord-serum concentrations of PCB 153 and DDE as continuous variables (per doubling exposure) and as cohort-specific tertiles. Summary estimates were obtained through random-effects meta-analyses.
The risk of bronchitis or wheeze (combined variable) assessed before 18 months of age increased with increasing DDE exposure (relative risk [RR] per doubling exposure = 1.03 [95% confidence interval = 1.00-1.07]). When these outcomes were analyzed separately, associations appeared stronger for bronchitis. We also found an association between increasing PCB 153 exposure and bronchitis in this period (RR per doubling exposure = 1.06 [1.01-1.12]) but not between PCB 153 and wheeze. No associations were found between either DDE or PCB 153 and ever-wheeze assessed after 18 months. Inclusion of both compounds in the models attenuated risk estimates for PCB 153 tertiles of exposure, whereas DDE associations were more robust.
This large meta-analysis suggests that prenatal DDE exposure may be associated with respiratory health symptoms in young children (below 18 months), whereas prenatal PCB 153 levels were not associated with such symptoms.
The presence in serum of antibodies to viral antigens is generally considered a well-defined marker of past infection or vaccination. However, analyses of serological data that use a cut-off value to classify individuals as seropositive are prone to misclassification bias, in particular when studying infections with a weak serological response, such as the sexually transmitted human papillomavirus (HPV).
We analyzed the serological concentrations of HPV type 16 (HPV16) antibodies in the general Dutch population in 2006-2007, before the introduction of mass vaccination against HPV. We used a 2-component mixture model to represent persons who were seronegative or seropositive for HPV16. Component densities were assumed to be log-normally distributed, with parameters possibly dependent on sex. The age-dependent mixing proportions were smoothed using penalized splines to obtain a flexible seroprevalence profile.
Our results suggest that HPV16 seropositivity is associated with higher antibody concentrations in women as compared with men. Seroprevalence shows an increase starting from adolescence in men and women alike, coinciding with the age of sexual debut. Seroprevalence stabilizes in men around age 40, whereas it has a decreasing trend from age 50 onwards in women. Analyses that rely on a cut-off value to classify persons as seropositive yield substantially different seroprevalence profiles, leading to a qualitatively different interpretation of HPV16 infection dynamics.
Our results provide a benchmark for examining the effect of HPV16 vaccination in future serological surveys. Our method may prove useful for estimating seroprevalence of other infections with a weak serological response.
The global impact of breast cancer is large and growing. It seems clear that something about modern life is the culprit, yet there is thus far a lack of satisfactory explanations for most of the increases in risk as societies industrialize. Support has developed for a possible role of "circadian disruption," particularly from an altered-lighted environment (such as light at night). Lighting during the night of sufficient intensity can disrupt circadian rhythms, including reduction of circulating melatonin levels and resetting of the circadian pacemaker of the suprachiasmatic nuclei. Reduced melatonin may increase breast cancer risk through several mechanisms, including increased estrogen production and altered estrogen receptor function. The genes that drive the circadian rhythm are emerging as central players in gene regulation throughout the organism, particularly for cell-cycle regulatory genes and the genes of apoptosis. Aspects of modern life that can disrupt circadian rhythms during the key developmental periods (eg, in utero and during adolescence) may be particularly harmful. Epidemiologic studies should consider gene and environment interactions such as circadian gene variants and shift work requirements on the job.
To study the combined effect of smoking and human papillomavirus (HPV) type 16 infection in high-grade cervical intraepithelial neoplasia, we analyzed data from a Norwegian population-based case-control study including 90 patients and 216 controls, 20-44 years of age. We assessed HPV-16 status both by polymerase chain reaction detecting virus DNA and by enzyme-linked immunosorbent assay detecting antibodies against virus capsid. Smoking was associated with cervical intraepithelial neoplasia grade II-III in HPV-16-positive individuals. Using the jointly unexposed (HPV-16 DNA-negative never-smokers) as the reference group, we determined the risk of cervical intraepithelial neoplasia grade II-III in HPV-16 DNA-positive never-smokers and HPV-16 DNA-positive ever-smokers (odds ratio = 15.7; 95% confidence limits = 3.2, 76.5, and odds ratio = 65.9; 95% confidence limits = 22.3, 194.3, respectively). The estimated proportion of cases among HPV-16-positive smokers that is attributable to the interaction between the two causes is 74%, based on HPV-16 DNA positivity.
We studied the relations between body height, body mass index (BMI), and fatal hip fractures prospectively in a large, representative population. During the years 1963-1975, a nationwide compulsory mass x-ray examination including standardized height and weight measurements took place in Norway covering all persons age 15 years and older. In the study presented here, we selected women (N = 357,807) and men (N = 316,041) age 50-89 years at screening. We matched the file to the national death register containing causes of death throughout 1991; we defined cases as persons with hip fracture mentioned on their death certificates. During an average follow-up of 16.4 years, we identified a total of 6,087 fatal hip fractures in the study population. There was a distinct inverse relation between BMI and fatal hip fracture, with an age-adjusted relative risk (RR) in the three highest vs the low quartile of 0.68 [95% confidence interval (CI) = 0.63-0.72] in women and 0.57 (95% CI = 0.52-0.62) in men. The risk of fatal hip fractures increased slightly with increasing body height [RR = 1.10 (95% CI = 1.04-1.16) in women and RR = 1.08 (95% CI = 1.01-1.16) in men per 10-cm increase in body height]. This study indicates that low BMI is an important risk factor for fatal hip fractures and that body height has a weak, positive association.
Between 1600 and 1700, sudden, profound, and multifarious changes occurred in philosophy, science, medicine, politics, and society. In an extremely convulsed century, these profound and convergent upheavals produced the equivalent of a cultural big bang, which opened a new domain of knowledge acquisition based on population thinking and group comparisons. In 1662, when John Graunt applied-for the first time-the new approach to the analysis of causes of death in London, he gave epidemiology a singular date of birth. This was exactly 350 years ago.
Elective cesarean delivery is increasingly common. The potential effects of surgical delivery in an unselected sample of infants beyond the immediate neonatal period remain poorly defined.
We carried out an 18-month follow-up of a population-based cohort of 8327 Hong Kong Chinese infants born in 1997. The main outcome measures were utilization of outpatient visits and hospitalizations, categorized by doctor-diagnosed causes as reported by parents.
Among term singleton infants, there was no association of cesarean (compared with vaginal) birth with subsequent hospital admission (adjusted odds ratio = 0.92; 95% confidence interval = 0.79-1.08) or with above versus below the median number of outpatient episodes (1.10; 0.96-1.26) in the first 18 months of life. There were weak positive associations with afebrile gastrointestinal, respiratory, skin and a few other conditions.
Cesarean birth is not associated with hospitalization or outpatient care overall during the first 18 months after adjustment for confounders. We cannot rule out isolated associations with minor morbidities.
We examined suspected risk factors for depression among adults ages 18-44 years. The subjects, selected by probability sampling for a multisite collaborative study, were interviewed at baseline and again at follow-up after one year. The risk of major depression was higher for women as compared with men (RR = 1.5), and for the maritally separated or divorced versus all other adults (RR = 1.9), but at lower levels for employed men and women as compared with the unemployed (RR = 0.6). Sex and marital separation or divorce also were associated with increased risk of a less specific and severe depressive syndrome; working for pay was associated with lower risk. In addition, risk of the depressive syndrome was lower for Hispanic Americans versus all other persons (RR = 0.3), and there was an important interaction of age and sex. With increasing age, women were at increasingly higher risk for the depressive syndrome, as compared with men. Finally, the risk of simple depression was higher for women than for men (RR = 1.8), but was not strongly associated with other suspected risk factors under study once sex was taken into account.
The evidence on whether breast-feeding reduces health services use in nonwhite infants is scant. We examined the effects of breast-feeding on health services utilization in Hong Kong Chinese infants.
We followed a population-based cohort of 8327 infants born in 1997 for 18 months. The main outcome measures were higher (above the sample mean) utilization of outpatient visits and hospitalizations for jaundice, gastrointestinal or respiratory/febrile illnesses, and all illnesses.
Breast-fed infants had fewer illness-related doctor visits overall through the first 18 months of life. Results were strongest for infants breast fed exclusively for 2 to 3 months (odds ratio [OR] for higher utilization = 0.78; 95% confidence interval [CI] = 0.62-0.99) and for 4 or more months (0.65; 0.53-0.81). However, breast-fed infants were more likely to receive outpatient care for jaundice, particularly in the first 3 months of life (ORs ranging from 2.5 to 8.4). Any breast-feeding was also associated with more jaundice-related hospital admissions, the effects of which were most acute in the first 3 months of life. Compared with exclusively formula-fed infants, the OR (CI) for mixed breast- and formula-fed was 2.4 (1.7-3.5); for exclusive breast-feeding up to 1 month, 4.5 (2.7-7.6); for exclusive breast-feeding 2 to 3 months, 3.2 (1.8-5.7); and for exclusive breast-feeding 4 or more months, 3.4 (2.0-5.7).
Breast-feeding in Hong Kong Chinese infants reduces doctor visits overall, but increases both outpatient visits and hospitalizations for jaundice.
Several studies have shown that low blood pressure in individuals age 65 years and older is related to increased overall mortality. We hypothesize that this association is secondary to serious underlying illness, which has caused blood pressure reduction and, subsequently, has increased the risk of dying. Our study population was comprised of individuals age 20 years and older in the county of Nord Trøndelag in Norway, who were studied in a general health survey between 1984 and 1986. We had measurements of blood pressure, blood glucose, weight, height, and other information for 9,732 women and 8,290 men age 65 years or older. During approximately 6 years of follow-up, 2,122 women and 2,578 men died. For both genders, low systolic pressure was not associated with increased mortality, and the mortality curve did not display a J-shaped relation, after adjustment for age, marital status, body mass index, blood glucose, self-assessed health, use of antihypertensive medication, and history of diabetes and cardiovascular diseases. For diastolic pressure, however, women in the lowest category (< 75 mmHg) had an adjusted mortality rate ratio of 1.21 (95% confidence limits = 1.05, 1.39), compared with reference women (80-87 mmHg). Among men, the analogous mortality rate ratio was 1.16 (95% confidence limits = 1.02, 1.31). To reduce further the potential confounding between diastolic pressure and underlying illness, we excluded users of antihypertensive medication as well as the 2 first years of follow-up. After these procedures, the J-shaped mortality curve was not present among women, and it was substantially reduced among men. Thus, the results for both men and women indicated that the age-adjusted J-shaped relation between diastolic blood pressure and mortality was confounded with indicators of ill health, and that the often-found association between low diastolic blood pressure and increased mortality is indirect, possibly caused by serious underlying disease.
In 1844, before a large medical audience in London, John Hutchinson demonstrated the use of measurements of pulmonary function to predict disease. In contrast to standard practice at that time, he conducted an epidemiological investigation that would have been acceptable by today's standards, in which he examined over 2000 people and contrasted healthy and diseased cases. His data clearly indicated how, what he called, "vital capacity" predicted disease. Exploring the history of this young Victorian-era physician is both humbling and instructive for the modern epidemiologist, who has the advantages of the successes of ever more rapid, computer-based, technical approaches to evaluate existing data sources, and fewer opportunities to actually collect primary data from large number of patients using physiologic tools.
The declining prevalence of left-handed individuals with increasing age has led to two main avenues of hypotheses; the association is due either (1) to a birth cohort effect and/or an age effect caused by a switch to right-handedness with advancing age or (2) to mortality selection that reduces survival in left-handed individuals, or both. It is uncertain whether a cohort or age effect can explain the decline in age-related prevalence, and conflicting evidence exists in favor of the mortality hypothesis. We compared mortality in a subgroup of 118 opposite-handed twin pairs by counting in how many instances the right-handed twin died first. There was no evidence of differential survival between right-handed and non-right-handed individuals in the entire 1900-1910 cohort. With respect to the number of right-handed twins who died first, there was no material disadvantage among those who were not right-handed. In 60% (95% confidence interval = 49.0-71.5%) of dizygotic pairs, the right-handed twins died first. In 50% of monozygotic pairs, right-handed twins died first. The prevalence of not being right-handed was higher among males (9.2%) than females (6.5%); there was a similar frequency of non-right-handedness in monozygotic (8.0%) and dizygotic (7.8%) twins. We did not find evidence of excess mortality among non-right-handed adult twins in this follow-up study.
The first major case-control study, published by Janet Lane-Claypon in 1926, provided the first epidemiologic evidence that low fertility increases breast cancer risk. This study in the United Kingdom was replicated in 1931 by JM Wainwright using a US sample. Neither study used modern statistical inference to interpret their data. We have evaluated and reanalyzed data from both studies to assess the validity of the original conclusions about the etiology of breast cancer.
We abstracted data from the published contingency tables for age at menarche, age at menopause, parity, age at marriage (as a proxy for age at first birth), and duration of lactation for each childbirth (as a proxy for lifetime duration of lactation). Study-specific odds ratios and associated 95% confidence intervals were calculated.
Findings from the quantitative reanalysis were consistent with contemporary epidemiologic evidence for age at menopause, parity, age at first birth, and duration of lactation.
Lane-Claypon's scientific efforts, as manifested in the 1926 UK study, are an excellent example of how one investigator's work can help develop a field of scientific inquiry.
Review of four questions faced by pesticide epidemiologists from 1945 to 1988 shows a transition from maternal to paternal concerns in Agent Orange reproductive research, greater emphasis on accidents than suicide in acute-injury research, and an apparent focus away from diagnoses specific to women in both occupational mortality and cancer research. Further study of such historical research trends might assist both causal inference and the ethical evaluation of epidemiologic research.
This paper explores the relationship between 2 persons much involved in the development of modern epidemiology, Jacob Yerushalmy and Abraham M. Lilienfeld. The formation of that relationship is described and the resulting influences by each individual on the other's professional work are discussed. Interactions between these 2 men contributed to several areas of epidemiologic development, including the effects of misclassification on observational study data, elements of epidemiologic causal inference, population-based linked databases, and the adaptation of statistical techniques by the epidemiology community. The impact of their association and its implications for modern epidemiologists are considered.
Recent studies suggested that air pollution might be related to low birth weight. We tested this hypothesis on data from the British 1946 birth cohort. We found a strong association between birth weight and an air pollution index based on coal consumption. Babies born in the most polluted areas were on average 87 grams lighter than those born in the areas with the cleanest air. Adjustment for a number of sociodemographic factors did not change these estimates. While confounding by unmeasured factors cannot be ruled out, these historical data support the hypothesis that birth weight could be affected by air pollution.
Cape Breton County contains one of the most polluted areas in North America and is socioeconomically depressed. We evaluated mortality patterns in this area over the past 5 decades, focusing on life expectancy and life loss. Life loss refers to the difference in life expectancy of Cape Breton County residents and all Canadians, and was further broken down into disease-specific components using cause-eliminated life table methods. We observed lags in health of 20 to 25 years for residents of Cape Breton County. Life expectancy in some municipalities of Cape Breton County is reduced by more than 5 years. Life loss for these residents is greater than that of any single cause of death for Canadians. Life loss among Cape Breton County women is primarily attributable to cancer, and, among men, to cardiovascular diseases. Life loss from cancer is higher in the steel-producing communities; whereas life loss from respiratory diseases and lung cancer is higher in the coal mining communities. These (and other) decompositions of life loss disclose patterns in health deficiencies that give rise to etiologic hypotheses and provide clues and directions for prevention and interventions.
Over the 38-year period from 1950 through 1987, 1,434 Olmsted County, Minnesota women had a first unilateral oophorectomy, while 1,828 underwent bilateral oophorectomy (including 113 with a second unilateral oophorectomy). Most procedures (61% of unilateral and 87% of bilateral oophorectomies) were in conjunction with hysterectomy, and trends over time paralleled those reported for hysterectomy. Almost half of all operations (27% of unilateral and 63% of bilateral oophorectomies) were elective. The rise in bilateral oophorectomy rates over time (3.7 per 100,000 person-years per year, P = 0.016) was mostly due to elective procedures among older women, with both an increased frequency of surgery and a shift from unilateral to bilateral oophorectomy.
The assessment of leisure-time physical activity in four studies that used a similar questionnaire was carried out by the University of Minnesota between 1957-1960 and 1985-1987. Each study included adults living in the Upper Midwest. In men, age-adjusted leisure-time energy expenditure consistently increased over time, with the greatest increase occurring between 1957-1960 and 1974-1975. Much of this increase occurred in moderate and heavy intensity activity and was greater for white collar workers than for blue collar workers. The increase in the last period was similar for both classes of workers. Data were unavailable for women before 1980. Age-adjusted leisure-time physical activity in women also increased between 1980-1982 and 1985-1987. This increase was greater for blue collar than for white collar women. A major strength of these analyses is the last two surveys, which were specifically designed to assess time trends. Exact comparability of the earlier two surveys with the two latter surveys cannot be established; however, the use of the same detailed questionnaire across 30 years is unique. We conclude that leisure-time physical activity has been increasing for three decades, including substantial increases in vigorous activities.
Cockpit crew in civil aviation are exposed to several potential health hazards, among them cosmic ionizing radiation. To assess the influence of occupational and other factors on mortality we conducted a cohort study among cockpit crew.
All pilots and other cockpit personnel of two German airlines were traced through registries and other sources for the period 1960-1997. Standardized mortality ratios, with German population rates as the reference, were calculated. We estimated the individual radiation dose based on individual job histories and assessed dose-response trends in stratified and regression analyses.
We compiled a cohort of 6061 male cockpit personnel, yielding 105,037 person-years of observation. The maximum estimated individual radiation dose was 80.5 mSv. Among 255 deaths overall (standardized mortality ratio [SMR] = 0.48; 95% confidence interval [CI] = 0.42-0.54) there were 76 cancer deaths (SMR = 0.56; CI = 0.43 - 0.74). Most cancer and cardiovascular SMRs were reduced. A slight increase was seen for brain cancer (SMR = 1.68; CI = 0.66-3.62). Employment duration was associated with the all-cancer mortality in Poisson regression analyses. No other dose-response relation was found.
German cockpit crew have a low overall and cancer mortality. The role of occupational causes, and particularly cosmic radiation, appears limited.
Scant research has analyzed the health impact of abolition of Jim Crow (ie, legal racial discrimination overturned by the US 1964 Civil Rights Act).
We used hierarchical age-period-cohort models to analyze US national black and white premature mortality rates (death before 65 years of age) in 1960-2009.
Within a context of declining US black and white premature mortality rates and a persistent 2-fold excess black risk of premature mortality in both the Jim Crow and non-Jim Crow states, analyses including random period, cohort, state, and county effects and fixed county income effects found that, within the black population, the largest Jim Crow-by-period interaction occurred in 1960-1964 (mortality rate ratio [MRR] = 1.15 [95% confidence interval = 1.09-1.22), yielding the largest overall period-specific Jim Crow effect MRR of 1.27, with no such interactions subsequently observed. Furthermore, the most elevated Jim Crow-by-cohort effects occurred for birth cohorts from 1901 through 1945 (MRR range = 1.05-1.11), translating to the largest overall cohort-specific Jim Crow effect MRRs for the 1921-1945 birth cohorts (MRR ~ 1.2), with no such interactions subsequently observed. No such interactions between Jim Crow and either period or cohort occurred among the white population.
Together, the study results offer compelling evidence of the enduring impact of both Jim Crow and its abolition on premature mortality among the US black population, although insufficient to eliminate the persistent 2-fold black excess risk evident in both the Jim Crow and non-Jim Crow states from 1960 to 2009.
Increasing suicide rates among the oldest segments of the population, together with the increasing proportion of elderly in Western countries are sources of growing concern. I analyzed suicide trends among the elderly in Norway during the period 1966-1986. I used Poisson regression to analyze time trends on the basis of age, calendar period, and birth cohorts. Age and period affected the suicide rates for both sexes more than did cohort effects. Specific age-sex groups preferred specific methods of suicide.
We investigated birth defects (N = 4,565) reported to the Medical Birth Registry of Norway among 192,417 births between 1967 and 1991 to parents identified as farmers in five agricultural and horticultural censuses between 1969 and 1989. The prevalences at birth of all and specific birth defects deviated little from those among 61,351 births to non-farmers in agricultural municipalities. We classified exposure indicators on the basis of information provided at the agricultural censuses. The main hypotheses were that parental exposure to pesticides was associated with defects of the central nervous system, orofacial clefts, some male genital defects, and limb reduction defects. We found moderate increases in risk for spina bifida and hydrocephaly, the associations being strongest for exposure to pesticides in orchards or greenhouses [spina bifida: 5 exposed cases, odds ratio (OR) = 2.76, 95% confidence interval (CI) = 1.07-7.13; hydrocephaly: 5 exposed cases, OR = 3.49, 95% CI = 1.34-9.09]. Exposure to pesticides, in particular in grain farming, was also associated with limb reduction defects (OR = 2.50; 95% CI = 1.06-5.90). We also saw an association with pesticides for cryptorchism and hypospadias. We found less striking associations for other specific defects and pesticide indicators, animal farming, and fertilizer regimens.