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Activity Number: 315
Type: Contributed
Date/Time: Tuesday, August 4, 2009 : 10:30 AM to 12:20 PM
Sponsor: Section on Statistics in Epidemiology
Abstract - #305412
Title: Some Errors Frequently Occurring in Estimating the Required Sample Size in Cohort and Case-Control Studies
Author(s): Peng T. Liu*+
Companies: FDA
Address: 5100 Paint Branch Pkwy, College Part, MD, 20740,
Keywords: Sample Size ; Case-Control Study ; Assumption Violation ; Accuracy of Estimate ; Relative Risk ; Odds Ratio
Abstract:

The equation for testing the difference between two independent proportions forms the basis for estimating the required sample size for both cohort and case-control studies. Omitting key elements in risk estimation and making some improportion assumptions could seriously affect the accuracy of values found for two proportions. The errors frequently committed are: 1) ignoring the duration of the study in risk estimation, 2) assuming that the specific group disease or exposure rate is equal to the corresponding population rate, 3)confusing the size for detecting a relative risk with the size for detecting an odds ratio, and 4) misusing the pooled estimate of two proportions in hypothesis testing. In this article, we examine the impact of such errors on sample size decisions and provide some remedies.

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