Choosing screening instrument and cut-point on screening instruments. A comparison of methods

Aims: This study analyzes decisive measures of efficiency of a test, receiver operating characteristic (ROC) analysis and QROC analysis combined with considerations about clinical, health-economic, and ethical aspects when choosing screening instruments. Methods: Analyses of Common Mental Disorders Screening Questionnaire (CMD-SQ) and its subscales SCL-SOM, Whiteley-7, SCL-ANX4, SCL-DEP6, SCL-8, plus combinations, for early detection of psychiatric disorders, are the subject for this analysis. In all, 46.4% of 2,414 new people with continuous sickness absence for more than eight weeks over one year in a well-defined Danish population of 120,000 inhabitants participated in the study. The study was performed as a two phase study. All 1,121 persons in Phase 1 filled in the CMD-SQ. In Phase 2, a random subsample of Phase 1 on 337, the people were further examined by a psychiatrist using SCAN as gold standard. The analyses were performed as weighted analyses on Phase 2. Results: From 17 analyses it was shown that the efficiency of a test, ROC analyses, and QROC analyses resulted in different optimal scales and cut-points. The random possibility of a positive test or negative test in the population is discussed for efficiency and ROC analyses. QROC analyses correct for this by the relative k-values as decisive measures. However, QROC analyses may discard tests of value, all depending on the purpose of the test. Conclusions: In supplement to test statistics the capacity of services to follow up on screening, ethics, and health economy are issues that should be considered in deciding what rating scale and cut-point should be adopted.