{"doi":"10.1016/j.jclinepi.2008.05.014","title":"Synthesis of observational studies should consider credibility ceilings","abstract":"<h4>Objective</h4>Meta-analyses of observational studies often get spuriously precise results. We aimed to factor this skepticism in meta-analysis calculations.<h4>Study design and setting</h4>We developed a simple sensitivity analysis starting from the assumption that any single observational study cannot give us more than a maximum certainty c% (called credibility ceiling) that an effect is in a particular direction and not in the other. Each study included in meta-analysis is adjusted for different credibility ceilings c and the consistency of the conclusion examined. We applied the method in three meta-analyses of observational studies with nominally statistically significant summary effects (mortality with teaching versus nonteaching health care; risk of non-Hodgkin's lymphoma with hair dyes; mortality with omega-3 fatty acids).<h4>Results</h4>Between-study heterogeneity I(2) estimates dropped from 36%-72% without a ceiling effect to 0% with ceilings of 9%, 4%, and 4% in the three meta-analyses, respectively. Nominal statistical significance was lost with ceilings of 10%, 8%, and 11%, respectively. The likelihood ratios suggested that even with minimal ceiling effects, there was no strong support for the credibility of each of these three associations.<h4>Conclusions</h4>Consideration of credibility ceilings allows conservative interpretation of observational evidence and can be applied routinely to meta-analyses of observational studies.","journal":"Journal of Clinical Epidemiology","year":2009,"id":12581,"datarank":0.6166310796259968,"base_score":4.110873864173311,"endowment":4.110873864173311,"self_citation_contribution":0.6166310796259968,"citation_network_contribution":0.0,"self_endowment_contribution":0.6166310796259968,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":60,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.0408,"is_oa":false,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2009-02-01","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":2,"is_corresponding":false},{"id":6209,"name":"Georgia Salanti","orcid":"0000-0002-3830-8508","position":0,"is_corresponding":true}],"reference_count":23,"raw_metadata":null,"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":[]}