| 1. Title: The potential and limitations of epidemiological studies. Author: Vessey MP Source: In: Fertility regulation today and tomorrow, [edited by] E. Diczfalusy and M. Bygdeman. New York, New York, Raven Press, 1987. :197-204. (Serono Symposia Publications from Raven Press, Volume 36) Abstract: Full evaluation of a contraceptive method involves prolonged observation of large numbers of subjects to assess benefits and risks. This requires epidemiological evaluation. Such studies are limited by many considerations with regard to design, conduct, and interpretation. The 2 main epidemiological approaches are the experimental approach in which the subjects are allocated at random to the birth control method under evaluation or to a comparison group, and the observational approach in which subjects who have themselves chosen their contraceptive method are studied. Experimental approaches have major limitations. For example, randomized studies often deal with very highly selected populations. Thus, every participant must give informed consent and none can have contraindications to any of the contraceptive methods included in the trial. In practice, researchers have to depend on observational studies of which there are 2 main kinds--the case-control study and the cohort study. 1 important basic limitation of case-control studies is that they provide a direct estimate only of relative risk, not of absolute risk. Cohort studies are, in general, much easier to understand than case-control studies. Case-control studies are usually quick, cheap, and easy to do. They may be the only way to study rare diseases and each is concerned with only a single disease. Case-control studies often permit study in great depth, are subject to bias in selecting cases and controls, provide an estimate only of relative risk, cannot study variables that may be altered by the disease event, and may present recall and bias problems in measuring exposure. Cohort studies are usually slow, expensive and difficult to do. They are usually only practicable for fairly common diseases. Numbers usually preclude collection of highly detailed information on each subject. Cohort studies enable many different diseases to be studied at once, are generally less subject to bias, and provide information on both relative and absolute risk. With cohort studies, one can study variables altered by the disease event, and problems with recall and bias in measuring exposure are avoided. Language: English Keywords: DEVELOPED COUNTRIES | DEVELOPING COUNTRIES | CONTRACEPTION RESEARCH | CASE STUDIES | STUDY DESIGN | OBSTACLES | DATA ANALYSIS | COHORT ANALYSIS | RELIABILITY | CONTRACEPTION | COMPARATIVE STUDIES | Family Planning | Studies | Research Methodology | Organization and Administration | Measurement Document Number: 201603 |
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