Colonoscopy rarely misses polyps > or =10 mm, but the miss rate increases significantly in smaller sized polyps. The available evidence is based on a small number of studies with heterogeneous study designs and inclusion criteria.

A lthough the number of test evaluations in the literature is increasing, much remains to be desired in terms of methodology. A series of surveys have shown that only a small number of studies of diagnostic accuracy fulfil essential methodologic standards. 1-3Shortcomings in the design of clinical trials are known to affect results. The biasing effects of inadequate randomization procedures and differential dropout have been discussed and demonstrated in several publications.4-6 A growing understanding of the potential sources of bias and variation has led to the development of guidelines to help researchers and readers in the reporting and appraisal of results from randomized trials.7,8 More recently, similar guidelines have been published to assess the quality of reporting and design of studies evaluating the diagnostic accuracy of tests. For many of the items in these guidelines, there is no or limited empirical evidence available on their potential for bias. 9In principle, such evidence can be collected by comparing studies that have design deficiencies with studies of the same test that have no such imperfections. Several large metaanalyses have used a meta-regression approach to account for differences in study design.10-12 Lijmer and colleagues examined a number of published meta-analyses and showed that studies that involved nonrepresentative patients or that used different reference standards tended to overestimate the diagnostic performance of a test.13 They looked at the influence of 6 methodologic criteria and 3 reporting features on the estimates of diagnostic accuracy in a limited number of clinical problems.We conducted this study of a larger and broader set of meta-analyses of diagnostic accuracy to determine the relative importance of 15 design features on estimates of diagnostic accuracy. Methods Data sources: systematic reviewsAn electronic search strategy was developed to identify all systematic reviews of studies evaluating the diagnostic accuracy of tests that were published between January 1999 and April 2002 in MEDLINE (OVID and PubMed), EMBASE (OVID), the Database of Abstracts of Reviews of Effect (DARE) of the Centre for Reviews and Dissemination (www.york.ac.uk/inst/crd Evidence of bias and variation in diagnostic accuracy studiesBackground: Studies with methodologic shortcomings can overestimate the accuracy of a medical test. We sought to determine and compare the direction and magnitude of the effects of a number of potential sources of bias and variation in studies on estimates of diagnostic accuracy. Methods:We identified meta-analyses of the diagnostic accuracy of tests through an electronic search of the databases MEDLINE, EMBASE, DARE and MEDION (1999-2002). We included meta-analyses with at least 10 primary studies without preselection based on design features. Pairs of reviewers independently extracted study characteristics and original data from the primary studies. We used a multivariable metaepidemiologic regression model to investigate the direction and strength of the a...