{"doi":"10.1016/j.jclinepi.2015.03.017","title":"Small studies are more heterogeneous than large ones: a meta-meta-analysis","abstract":"<h4>Objectives</h4>Between-study heterogeneity plays an important role in random-effects models for meta-analysis. Most clinical trials are small, and small trials are often associated with larger effect sizes. We empirically evaluated whether there is also a relationship between trial size and heterogeneity (τ).<h4>Study design and setting</h4>We selected the first meta-analysis per intervention review of the Cochrane Database of Systematic Reviews Issues 2009-2013 with a dichotomous (n = 2,009) or continuous (n = 1,254) outcome. The association between estimated τ and trial size was evaluated across meta-analyses using regression and within meta-analyses using a Bayesian approach. Small trials were predefined as those having standard errors (SEs) over 0.2 standardized effects.<h4>Results</h4>Most meta-analyses were based on few (median 4) trials. Within the same meta-analysis, the small study τS(2) was larger than the large-study τL(2) [average ratio 2.11; 95% credible interval (1.05, 3.87) for dichotomous and 3.11 (2.00, 4.78) for continuous meta-analyses]. The imprecision of τS was larger than of τL: median SE 0.39 vs. 0.20 for dichotomous and 0.22 vs. 0.13 for continuous small-study and large-study meta-analyses.<h4>Conclusion</h4>Heterogeneity between small studies is larger than between larger studies. The large imprecision with which τ is estimated in a typical small-studies' meta-analysis is another reason for concern, and sensitivity analyses are recommended.","journal":"Journal of Clinical Epidemiology","year":2015,"id":1669,"datarank":0.8675737773494607,"base_score":5.783825182329737,"endowment":5.783825182329737,"self_citation_contribution":0.8675737773494607,"citation_network_contribution":0.0,"self_endowment_contribution":0.8675737773494607,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":324,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.0455,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2015-08-01","fair_score":61.25,"fair_percentile":92.70008795074759,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":18955,"name":"George F. 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