American journal of epidemiology
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Precise measurement of confounding or effect modifying variables is seldom possible. Nondifferential misclassification of such a variable can introduce bias in the odds ratios within the strata of the confounding variable. ⋯ For one stratum, the degree of bias introduced in the odds ratio is dependent only on the sensitivity of the measure of the confounding variable while only the specificity of this measure determines the bias introduced in the other stratum-specific odds ratio. The results are applied to a case-control study of fenoterol prescription and asthma death.
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It has been hypothesized that milk consumption increases the risk of ovarian cancer because of a possible association of lactose with human ovarian failure. Milk is also a source of animal fats in the diet, and animal fat intake is associated with ovarian cancer risk. To explore further the possible confounding of the milk-ovarian cancer association by the animal fat content of milk, the authors performed a case-control study of 303 ovarian cancer cases and 606 age-matched nonmalignant-disease controls seen between 1982 and 1988 at Roswell Park Memorial Institute in Buffalo, New York. ⋯ Among persons who reported drinking milk regularly, persons reporting drinking only whole milk were at increased risk (relative risk = 2.6, 95% CI 1.7-4.0) relative to persons who drank only skim milk or 2% milk. These findings suggest that milk-drinking is not a source of ovarian cancer risk independently of its fat content. Additional study of lactose and ovarian cancer risk involving careful control for confounding is needed.
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For men participating in the Multiple Risk Factor Intervention Trial, the authors evaluated the relation between the baseline forced expiratory volume in one second and lung cancer mortality among smokers between the third and tenth years of follow-up (1973-1974 to 1984). This measure of ventilatory function was a powerful predictor of lung cancer deaths, with rates that increased from 3.02 per 1,000 person-years in the lowest quintile of forced expiratory volume to 0.43 in the highest quintile. ⋯ Nor was forced expiratory volume related to time between its determination and lung cancer death. If these observations can be verified in other studies, the forced expiratory volume in one second may identify smokers at very high risk of lung cancer and, hence, in need of more aggressive preventive approaches.
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In a previous analysis from the Alameda County Study, it was observed that although men had higher heart disease mortality rates than women, there was no male excess in the prevalence of self-reported heart disease morbidity at baseline or in new reports of morbidity 9 years past baseline. This apparent contradiction might occur because women report less severe heart disease than men. In the present study, this hypothesis was evaluated by examining whether self-reported heart trouble was more strongly associated with subsequent heart disease mortality for men than for women in a representative sample of the population of Alameda County, California, selected in 1965 and followed for mortality for 19 years (n = 3,742). ⋯ Sex differences in the prognosis of self-reported heart trouble were masked in non-time-dependent analyses. These results illustrate that consideration of time dependence may be required for meaningful analysis of long-term cohort studies. Possible explanations of the shorter time to death for men who reported heart trouble are discussed.
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In 1984, a press release by a Miami, Florida, neurologist described a possible cluster of persons with multiple sclerosis in Key West, Florida. The authors examined the cluster using prevalence rates, which are recognized as having a latitudinal gradient for multiple sclerosis, being generally high at high latitudes and low at low latitudes. ⋯ Prevalent cases (n = 22) were more likely than general population controls (n = 76), matched by sex and 10-year age group, to have: lived longer in Key West, been a nurse, ever owned a Siamese cat, had detectable antibody titers to coxsackievirus A2 and poliovirus 2, and ever visited a local military base (Fleming Key). Key West has an unusually high prevalence of multiple sclerosis that may be related to these risk factors.