Radiographers and other healthcare professionals are becoming increasingly involved in radiological reporting, for instance plain radiographs, mammography and ultrasound. Systematic reviews of research evidence can help to assimilate a knowledge base by ordering and evaluating the available evidence on the reporting accuracy of different professional groups. This article reviews the biases that can undermine the results of plain ¿lm reading performance studies. These biases are subdivided into three categories. The ¿rst category refers to the selection of subjects, including both ¿lms and professionals, and covers the validity of generalizing results beyond the study population. The other two categories are concerned with study design and the interpretation both of ¿lms and of reports and the effect on study validity. An understanding of these biases is essential when designing such studies and when interpreting the results of existing studies.