Methodological issues in mammography double reading studies

OBJECTIVES: An examination of the methods used in assessing cancer detection rates in double reading studies to obtain a clear interpretation of the disparate results from differing studies. SETTING: National breast screening programmes. METHODS: Critical appraisal of methodologies used in the comparison of cancer detection rates with single or double reading. RESULTS: The reported improvement in cancer detection rate with double reading varies greatly between studies, depending upon whether the study is blinded and the statistic used. A method of calculating the increase in cancer detection rate due to a second reader is proposed.