Working Procedures


4. Efficacy of screening tests

In this section, evidence from epidemiological studies is reviewed, and aspects of study design and analysis are critically discussed. The Handbooks are not intended to summarize all published studies (see Part A). The Working Group considers the following aspects:

  • Relevance of the study;
  • Appropriateness of the design and analysis to the question being asked;
  • Adequacy and completeness of the presentation of the data;
  • Degree to which chance, bias, and confounding may have affected the results.

The appropriate outcomes (mortality or incidence) of a given procedure, for example the detectable phases of the natural history of the disease, are also defined.

Aspects that are particularly important in evaluating randomized controlled trials are: the selection of participants, the nature and adequacy of the randomization procedure, evidence that randomization achieved an adequate balance between the groups, the exclusion criteria used before and after randomization, compliance with the intervention in the screened group, and “contamination” of the control group with the intervention. Other considerations are the means by which the end-point was determined and validated (either by screening or by other means of detection of the disease), the length and completeness of follow-up of the groups, and the adequacy of the analysis.

Whenever possible, similar criteria should be used to evaluate other observational studies. In evaluating case–control and cohort studies, particular attention is paid to the definition of cases, controls, and exposure and, for cohort studies, to the length and completeness of follow-up. Potential bias, especially selection bias, is carefully examined in all observational studies.


Posted 27 May 2014