Effect of experimental design on sample size

An increasing practical problem in the evaluation of the accuracy of new imaging systems, as well as the effect of modifications in the display of current imaging systems, is the effort entailed in performing the necessary readings. Although some constraints are dictated by the specific evaluation being conducted, some aspects of the experiment can be determined by the investigator. These include, but are not limited to, the method used to select the cases (selected, stratified, or random) and whether continuous variables that are being evaluated (i.e., pixel size, brightness, contrast) are grouped into discrete categories. The selection of the experimental design has an impact on the sample size required to answer the study question and thus impacts on the cost and effort required to do the study.