Abstract
IntroductionMany diagnostic accuracy studies are never reported in full in a peer‐reviewed journal. Searching for unpublished studies may avoid bias due to selective publication, enrich the power of systematic reviews, and thereby help to reduce research waste. We assessed searching practices among recent systematic reviews of diagnostic accuracy.MethodsWe extracted data from 100 non‐Cochrane systematic reviews of diagnostic accuracy indexed in MEDLINE and published between October 2017 and January 2018 and from all 100 Cochrane systematic reviews of diagnostic accuracy published by December 2018, irrespective of whether meta‐analysis had been performed.ResultsNon‐Cochrane and Cochrane reviews searched a median of 4 (IQR 3‐5) and 6 (IQR 5‐9) databases, respectively; most often MEDLINE/PubMed (n = 100 and n = 100) and EMBASE (n = 81 and n = 100). Additional efforts to identify studies beyond searching bibliographic databases were performed in 76 and 98 reviews, most often through screening reference lists (n = 71 and n = 96), review/guideline articles (n = 18 and n = 52), or citing articles (n = 3 and n = 42). Specific sources of unpublished studies were searched in 22 and 68 reviews, for example, conference proceedings (n = 4 and n = 18), databases only containing conference abstracts (n = 2 and n = 33), or trial registries (n = 12 and n = 39). At least one unpublished study was included in 17 and 23 reviews. Overall, 39 of 2082 studies (1.9%) included in non‐Cochrane reviews were unpublished, and 64 of 2780 studies (2.3%) in Cochrane reviews, most often conference abstracts (97/103).ConclusionSearching practices vary considerably across systematic reviews of diagnostic accuracy. Unpublished studies are a minimal fraction of the evidence included in recent reviews.
Highlights
Among systematic reviews of therapeutic interventions, it has been documented that published trials report, on average, a 9% greater treatment effect than unpublished ones.[4]
In this evaluation, unpublished studies were defined as those that had not been reported in full in a peer-reviewed journal but had only been described or mentioned in, for example, conference abstracts, trial registries, dissertations, repositories, book chapters, or unpublished manuscripts obtained through contact with investigators
MEDLINE had been searched for systematic reviews of diagnostic accuracy published between 31 October 2017 and 20 January 2018, where the time span had been modulated to reach a convenience sample size of 100 systematic reviews, using the following search strategy: “systematic[sb] AND.”
Summary
Many diagnostic accuracy studies are never reported in full in a peer-reviewed journal. We assessed searching practices among recent systematic reviews of diagnostic accuracy. Conclusion: Searching practices vary considerably across systematic reviews of diagnostic accuracy. Unpublished studies are a minimal fraction of the evidence included in recent reviews. Unpublished studies are often difficult to identify, making the inclusion of their results in systematic reviews a hazardous task. This may lead to flawed and overoptimistic review conclusions, when studies with more optimistic results are published more often. A number of evaluations assessed publication rates among completed diagnostic accuracy studies, identifying that approximately a quarter to half of them failed to reach full-text publication in a peer-reviewed journal.[5-9]. Two studies evaluated time from study completion to publication among published diagnostic accuracy studies, both concluding that those reporting higher estimates of diagnostic accuracy were published more rapidly.[10,11] It seems plausible that studies reporting higher estimates of diagnostic accuracy more often reach publication, this has yet to be demonstrated.[6-9]
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