American Journal of Epidemiology Vol. 124, No. 1: 134-149
Copyright © 1986 by The Johns Hopkins University School of Hygiene and Public Health
research-article |
DURATION OF DISEASE, DURATION INDICATORS, AND ESTIMATION OF THE RISK RATIO
1Hospital Epidemiology Unit, Channing Laboratory, Department of Medicine, Harvard Medical School, Boston City Hospital, and Peter Bent Brigham Hospital, Division of Brigham and Women's Hospital Boston, MA
2Department of Epidemiology, Harvard School of Public Health Boston, MA
Reprint requests to Dr. Jonathan Freeman, Channing Laboratory, 180 Longwood Avenue, Boston, MA 02115
The authors investigated how duration of disease and duration of risk until onset of disease relate prevalence odds ratios and cumulative incidence ratios, respectively, to incidence density ratios in a steady-state population. Using information on durations, they demonstrated how incidence density ratios may be estimated from the information availabie in variants of the case-referent study and their cohort study analogues. The standard case-referent study involves an incidence series of cases and a prevalence series of noncases. One variant is a study of a prevalence series of cases and a prevalence series of noncases. Another variant involves comparison of two incidence series for sequential incident events. Factors associated with disease risk have been termed risk Indicators, and, by analogy, factors associated with disease duration are defined as duration indicators. These duration indicators may be identified through the study of duration ratios. Ratios of durations in steady-state poputations may be combined with the prevalence and cumulative incidence information available in the variants of the standard study designs to obtain estimates of incidence density ratios.
epidemiologic methods; prevalence studies; research design