- This study compares matched and unmatched case-control designs in terms of the precision with which one can estimate an exposure-disease association while controlling for the effects of a confounding variable. Provision is made for the cost of the matching process by calculating the reduction in the number of controls that can be studied for fixed study cost. The purpose is to provide epidemiologists with guidelines and quantitative procedures for making rational decisions as to which is the more appropriate study design for specific research problems. The results indicate that when the cost of the matching process is negligible, a matched design is usually more efficient than an unmatched one. The difference in efficiency is generally slight, however, and is found to depend primarily on the strength of the confounder-disease association, the prevalence of exposure, and the strength of the exposure-disease association. When the cost of the matching process is not negligible, a matched design is likely to be less efficient than an unmatched one.