Epidemiology
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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. ⋯ 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.
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We investigated the trends in age-standardized rates (per 100,000 persons-years) of unintentional injury deaths in adult Finns from 1971-1997. In 1971, the leading category of unintentional injury resulting in death among Finnish men was road traffic accidents (age-standardized death rate 47 per 100,000 person-years). This rate has declined sharply, reaching 13 per 100,000 person-years in 1997. ⋯ Concurrently the rate of fall-induced deaths in women also decreased, from 27/100,000 person-years in 1971 to 17/100,000 person-years in 1997. Falling, however, was the leading cause of injury-related death in 1997. Thus, in the period 1971-1997, falls replaced road traffic accidents as the leading cause of unintentional injury death in Finland.
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Standard methods for survival analysis, such as the time-dependent Cox model, may produce biased effect estimates when there exist time-dependent confounders that are themselves affected by previous treatment or exposure. Marginal structural models are a new class of causal models the parameters of which are estimated through inverse-probability-of-treatment weighting; these models allow for appropriate adjustment for confounding. We describe the marginal structural Cox proportional hazards model and use it to estimate the causal effect of zidovudine on the survival of human immunodeficiency virus-positive men participating in the Multicenter AIDS Cohort Study. ⋯ After controlling for baseline CD4 count and other baseline covariates using standard methods, the mortality rate ratio decreased to 2.3 (1.9-2.8). Using a marginal structural Cox model to control further for time-dependent confounding due to CD4 count and other time-dependent covariates, the mortality rate ratio was 0.7 (95% conservative confidence interval = 0.6-1.0). We compare marginal structural models with previously proposed causal methods.
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We studied the possible environmental factors in the origin of microcephaly by comparing the exposures of 109 infants with isolated microcephaly with those of two matched population controls, in addition to those of 812 patient controls (that is, infants with Down syndrome). Cases and patient controls were selected from the large population-based dataset of the Hungarian Case-Control Surveillance of Congenital Abnormalities registered between 1980 and 1996, whereas matched population controls were selected from the national birth registry. We found that there were more females than males among cases with isolated microcephaly. ⋯ The use of clotrimazole was higher among mothers in the matched population control group than among mothers of cases. Maternal use of a large dose (about 6 mg per day) of folic acid and more than 50 mg per day of iron during pregnancy was associated with a 40-50% decrease in microcephaly. Thus, the pharmacological doses of folic acid and iron may have some preventive effect against isolated primary microcephaly.
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Both the incidence of and mortality from bleeding and perforated peptic ulcers are increasing. We assessed the association between smoking, intake of alcohol (including type of alcoholic beverage), and risk of a complicated peptic ulcer in a population-based study of 26,518 Danish subjects followed up for an average of 13.4 years. There were 214 cases of incident bleeding and 107 cases with perforated ulcers. ⋯ Smoking more than 15 cigarettes per day compared with never smoking increased the risk of a perforated ulcer more than threefold [RR = 3.5; 95% confidence interval (CI) = 1.7-7.1)]. Drinking more than 42 drinks per week increased the risk of a bleeding ulcer fourfold (RR = 4.4; 95% CI = 2.3-8.3) compared with drinking less than one drink per week. Using the same comparison group, subjects who drank more than 21 drinks per week but no wine were at a higher risk of a bleeding ulcer (RR = 8.8; 95% CI = 2.2-35) than drinkers of the same amount of alcohol, but with more than 25% of their intake as wine (RR = 2.4; 95% CI = 1.0-6.0).