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Control-initiated case-control studies.

S Greenland
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Abstract

In a control-initiated study the investigator begins with existing data on a non-diseased group and then selects cases to obtain comparison data; thus the usual order of case and control selection is reversed. This paper discusses the parallels and differences between control-initiated studies and more traditional case-control designs. Special attention is given to problems of selection bias and matching. A sample-size formula for control-initiated studies is also provided.

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Epidemiologic MethodsHumansResearch DesignRiskStatistics as TopicJournal ArticleResearch Support, U.S. Gov't, P.H.S.

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BibTeXRIS

S Greenland. 1985. Control-initiated case-control studies.. https://doi.org/10.1093/ije%2F14.1.130

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Temporal change in the reproducibility of a self-administered food frequency questionnaire.

The authors studied temporal change in the reproducibility of a self-administered food frequency questionnaire. During 1988-1994, 492 residents of a rural Japanese town completed five questionnaires including 27 food items, with intervals ranging from 2 weeks through 5.5 years. The reproducibility decreased steadily over time for pairs of the questionnaires administered in the same season (median Spearman's r at 2 weeks and 5 years = 0.62 and 0.28, respectively). The reduction was less marked for those surveyed in different seasons (median r at 5 months and 5.5 years = 0.35 and 0.28, respectively). The short-term, different season correlation at 5 months was lower than the short-term, same season correlation at 1 year. For individual food items, a lower initial reproducibility, infrequent consumption, and a larger difference in seasonal intake were associated with a greater reduction in reproducibility over time. The results indicate that reproducibility studies should deliberately choose the intervals and the seasons for surveys.

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