Endodontic Meta-analyses: Accuracy of National Library of Medicine’s Classification

Background:  Correctly indexed and classified published articles are important particularly in regards to evidence-based practice.  PubMed is the National Library of Medicine’s online interface to Medline in which articles are indexed and searchable by publication type filters. 

Objectives: To determine the percentage of endodontic-related meta-analyses that are indexed in PubMed, and of those indexed, what proportion are correctly classified as meta-analysis publication type.

Methods: From May 15 – August 14, 2011, PubMed searches were performed for the terms “meta analysis AND endodontics” (without Limits).  Articles were reviewed to determine how many were indexed as a meta-analysis and how many were correctly classified as a meta-analysis publication type. In other words, articles were reviewed to determine how many indexed meta-analysis completed a meta-analysis.

Results:  The search identified 74 potential endodontic meta-analyses, and of these, 51 were indexed in PubMed as meta-analyses.  Of the 51, 69% (95% CI: 54 to 81) were correctly indexed as a meta-analysis, i.e., the article actually reported on results from a meta-analysis.  The most common problem found was that a meta-analysis was discussed or initially planned but not performed due to lack of data or heterogeneity of data and ended up being a systematic review instead. 

Conclusion: The National Library of Medicine’s “publication type” classification for endodontic-related meta-analyses appears to be correct only about 70% of the time.  This has serious implications for evidence-based hierarchical search strategies.  It should be noted that our results are limited to the field of Endodontics,  However, comparable misclassifications of meta-analyses were reported for a sample of orthodontic articles last year (Shin et al., 2010) Further studies on the accuracy of indexing of meta-analyses are currently in process in Periodontics.