Screening: part 19 of a series on evaluation of scientific publications.

BACKGROUND The early detection of cancer and other diseases is generally considered beneficial, yet there is evidence that in some diseases screening may be of limited benefit. To clarify this issue, we present the statistical principles that underlie screening. Methods We define screening and discuss the conditions for its successful use. We give illustrative examples from among the currently recommended types of screening in Germany and from the recent medical literature, particularly with regard to mammography. RESULTS Certain specific conditions must be fulfilled for screening to be beneficial (usually measured by reduced mortality): The screening procedure must be of high quality, and the screening intervals must be well adapted to the distribution of the sojourn time. Alongside its benefits, screening can also cause harm, particularly to the many patients who are given a false positive test result. According to German law, potential participants are entitled to being given all information necessary to make an informed decision about screening. CONCLUSION Just like clinical interventions, screening programs should be evaluated before they are introduced or, at the latest, at the time of their introduction.