SAMPLE SIZE DETERMINATION FOR CASE CONTROL STUDIES

INTRODUCTION: In a typical case–control study, cases of a specific disease are ascertained as they arise from data collection tools which may include population-based registers or lists of hospital admissions, and controls are sampled either as disease-free people from the population at risk, or as hospitalized patients having a diagnosis other than the one under study. Then in the analysis, we compare the exposure histories of the two groups. In other words, a typical case–control study fits the framework of a two-arm randomized phase III trials. Phases of clinical trials  

It should however be note that, the sample determination is somewhat more complicated, for three reasons: 

(1) Instead of searching for a difference of two means or proportions as in the case of a phase III trial, the alternative hypothesis of a case–control study is postulated in the form of a relative risk.  

(2) It must be decided whether to design a study with equal or unequal sample sizes because in epidemiologic studies, there are typically a small number of cases and a large number of potential controls to select from. Research study designs  

(3) It must be decided whether to design a matched or an unmatched study. For example, we may want to design a case–control study to detect a relative risk, due to a binary exposure, of 2.0, and the size of the control group is twice the number of the cases. 

RELATED;

1.  Sample size calculation  

2.  The case study design

3.  Calculation of sample size-formula 4

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