This study focused on the factors that have an impact on the clinical efficacy of diagnostic laboratory tests. A new graphical method (cost-error plot) was developed to demonstrate prevalence and costs of misclassification on test performance, two important factors that affect the practical usefulness of diagnostic tests. Unlike receiver operating characteristic plots, the clinical efficacy of laboratory tests can be readily compared by cost-error plots over a range of possible prevalences and misclassification costs. A manuscript of the study is being prepared. Future work will focus on developing software to facilitate production of cost-error plots.