ABSTRACT
INTRODUCTION It has already been noted that to make the best use of limited resources it is necessary to select a sample of an appropriate size. This decision needs to be made when the study is planned and is based on a samplesize calculation. A statement about the estimated size of the sample required for a study is usually requested by funding organizations and ethical committees when a project proposal is assessed. Sample-size calculation generally involves quite complicated algebra; the interested reader should consult a detailed text on medical statistics, such as Armitage, Berry, and Matthews (2001).
