PubMed · 7310016
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Z Stein, M Susser. 1981. Methods in epidemiology.. https://doi.org/10.1016/s0002-7138(09)61639-3
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Several approaches have been proposed to model binary outcomes that arise from longitudinal studies. Most of the approaches can be grouped into two classes: the population-averaged and subject-specific approaches. The generalized estimating equations (GEE) method is commonly used to estimate population-averaged effects, while random-effects logistic models can be used to estimate subject-specific effects. However, it is not clear to many epidemiologists how these two methods relate to one another or how these methods relate to more traditional stratified analysis and standard logistic models. The authors address these issues in the context of a longitudinal smoking prevention trial, the Midwestern Prevention Project. In particular, the authors compare results from stratified analysis, standard logistic models, conditional logistic models, the GEE models, and random-effects models by analyzing a binary outcome from two and seven repeated measurements, respectively. In the comparison, the authors focus on the interpretation of both time-varying and time-invariant covariates under different models. Implications of these methods for epidemiologic research are discussed.
The authors report on the changing incidence of and maternal mortality from ectopic pregnancies in Hungary between 1931 and 1995. Data of reported pregnancies were obtained from the National Institute of Statistics and the Hungarian College of Obstetricians and Gynecologists. Incidence of ectopic pregnancy was calculated as rates per 1000 live births and per 1000 reported pregnancies including live births, legally induced abortions, miscarriages, and ectopic pregnancies. Ectopic pregnancy-associated maternal mortality was examined in terms of case fatality rate and also as a proportion to the total number of pregnancy-associated maternal deaths. From 1931, when national surveillance for pregnancy begun in Hungary, to 1995, the rate per 1000 reported live births tripled from 3.4 to 11.9. Similarly, the rate of ectopic pregnancies per 1000 reported pregnancies increased by 190% from 3.7 to 6.4. In the last decade of the period studied, its proportion in the annual number of fetal deaths increased to 8.0%. Ectopic pregnancy-associated maternal deaths decreased sharply from 1931 through the late 1980's. In the last decade, its average value was 16 per 10.000 reported ectopic pregnancies. However, case fatality rate of ectopic pregnancy is still highest compared to any of the other obstetric events including induced and spontaneous abortions, and deliveries. Over the last decade, maternal deaths resulting from ectopic gestation represented 8.7% of the total maternal mortality rate. Given the increasing incidence of ectopic pregnancy together with a substantial proportion in pregnancy-related maternal mortality, study of etiology, and appropriate preventive measures are urgently needed.