CASE-CONTROL STUDIES OF CANCER SCREENING - THEORY AND PRACTICE

This review summarizes methodologic theories for the design of cancer screening case-control studies and examines the methods applied in stu dies published in English from 1980 through 1996, In addition to summa rizing state-of-the-art methodologic approaches, we identify areas whe re obvious gaps exist between theory and practice, and we recommend po tential areas where theory and methodology may need further developmen t, In particular, we focus on three major areas: 1) the selection of c ase and control subjects, 2) the definition of exposure (i.e., exposur e to the screening test), and 3) bias, Each area is considered careful ly by summarizing current theory, reviewing cancer screening applicati ons, and linking recommended methodologic approaches to those used in practice to identify areas where inconsistencies exist. In general, we found methodologic theory and practice in this field of research to b e consistent. However, discrepancies were identified in the area of ex posure definition, including the use of screening frequency and the us e of a detectable, curable preclinical phase for case subjects as the exposure measures, Even when recommended methods were followed, a numb er of difficulties arose in practice, Specific concerns included the a bility to carry out the following: identifying all case subjects withi n a source population, defining eligibility criteria to ensure that ca se and control subjects had equal access to screening during the expos ure period, distinguishing between symptomatic and diagnostic tests, a nd controlling for self-selection bias, Careful scrutiny is warranted in all aspects of the design of cancer screening case-control studies, and caution is advised in the interpretation of study results.