Estimating the duration of ongoing prevention trials

Timothy R. Church, Fred Ederer, Jack S. Mandel, Gavin D. Watt, Mindy S. Geisser

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


The authors present a method of estimating the duration of ongoing prevention trials, showing how the method was applied to the Colon Cancer Control Study, a University of Minnesota study of occult blood testing undertaken to screen for colorectal cancer in older Minnesotans. In that study, begun in 1975 and ongoing, as in several other recent large prevention trials, it was necessary, after the start of the study, to revise upward the initial estimates of study duration derived from general population experience. The underestimates arose because the planners had not adequately taken various population selection factors into account in estimating the expected number of events in the control group. In this paper, the authors outline a method for estimating control group event rates and study duration requirements (and, in some circumstances, also sample size requirements) of prevention studies, via models of disease-specific and all-cause standardized mortality ratios which adjust for various selection effects. The authors also validate the model for disease-specific standardized mortality ratios by means of independent estimates of disease incidence and case survival.

Original languageEnglish (US)
Pages (from-to)797-810
Number of pages14
JournalAmerican journal of epidemiology
Issue number7
StatePublished - Apr 1 1993

Bibliographical note

Funding Information:
Received for publication August 12, 1991, and in final form October 13, 1992. Abbreviations: SEER, Surveillance, Epidemiology, and End Results; SMR, standardized mortality ratio. 1Division of Environmental and Occupational Health, School of Public Health, University of Minnesota, Minneapolis, MN. 2 Division of Btostatistjcs, School of Public Health, University of Minnesota, and The EMMES Corporation, Potomac, MD. Reprint requests to Dr. Timothy R. Church, School of Public Health, University of Minnesota, 212 Ontario Street SE, Suite 202, Minneapolis, MN 55414. This study was supported by contracts from the National Cancer Institute (NOI-CB-61005 and NOK8-95613).


  • Clinical trials
  • Colorectal neoplasms
  • Epidemiologic methods
  • Incidence
  • Mortality
  • Randomized controlled trials
  • Research design
  • Selection bias


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