{"doi":"10.1016/j.jclinepi.2010.12.012","title":"Statistically significant meta-analyses of clinical trials have modest credibility and inflated effects","abstract":"<h4>Objective</h4>To assess whether nominally statistically significant effects in meta-analyses of clinical trials are true and whether their magnitude is inflated.<h4>Study design and setting</h4>Data from the Cochrane Database of Systematic Reviews 2005 (issue 4) and 2010 (issue 1) were used. We considered meta-analyses with binary outcomes and four or more trials in 2005 with P<0.05 for the random-effects odds ratio (OR). We examined whether any of these meta-analyses had updated counterparts in 2010. We estimated the credibility (true-positive probability) under different prior assumptions and inflation in OR estimates in 2005.<h4>Results</h4>Four hundred sixty-one meta-analyses in 2005 were eligible, and 80 had additional trials included by 2010. The effect sizes (ORs) were smaller in the updating data (2005-2010) than in the respective meta-analyses in 2005 (median 0.85-fold, interquartile range [IQR]: 0.66-1.06), even more prominently for meta-analyses with less than 300 events in 2005 (median 0.67-fold, IQR: 0.54-0.96). Mean credibility of the 461 meta-analyses in 2005 was 63-84% depending on the assumptions made. Credibility estimates changed >20% in 19-31 (24-39%) of the 80 updated meta-analyses.<h4>Conclusions</h4>Most meta-analyses with nominally significant results pertain to truly nonnull effects, but exceptions are not uncommon. The magnitude of observed effects, especially in meta-analyses with limited evidence, is often inflated.","journal":"Journal of Clinical Epidemiology","year":2011,"id":7684,"datarank":7.130290792220957,"base_score":5.081404364984463,"endowment":5.081404364984463,"self_citation_contribution":0.7622106547476696,"citation_network_contribution":6.368080137473287,"self_endowment_contribution":0.7622106547476696,"citer_contribution":6.368080137473287,"corpus_percentile":null,"corpus_rank":null,"citation_count":160,"citer_count":144,"citers_with_citation_signal":125,"citers_with_endowment":125,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.0614,"is_oa":false,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2011-10-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":148,"name":"John P. A. Ioannidis","orcid":"0000-0003-3118-6859","position":3,"is_corresponding":false},{"id":15114,"name":"Tiago V. Pereira","orcid":"0000-0002-8574-832X","position":0,"is_corresponding":true}],"reference_count":65,"raw_metadata":{"citation_network_status":"fetched"},"created_at":"2026-03-01T18:20:47.508186Z","pmid":null,"pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}