{"doi":"10.1093/ije/dym001","title":"Evidence from crossover trials: empirical evaluation and comparison against parallel arm trials","abstract":"<h4>Background</h4>We aimed to evaluate empirically how crossover trial results are analysed in meta-analyses of randomized evidence and whether their results agree with parallel arm studies on the same questions.<h4>Methods</h4>We used a systematic sample of Cochrane meta-analyses including crossover trials. We evaluated the methods of analysis for crossover results and compared the concordance of the estimated effect sizes in crossover vs parallel arm trials.<h4>Results</h4>Of 334 screened reviews, 62 had crossover trials. Of those, 33 meta-analyses performed quantitative syntheses involving two-arm two-period crossover trials. There was large variability on how these trials were analysed; only one of the 33 meta-analyses stated that they used the data from both the first and second period with an appropriate paired approach. Nine meta-analyses used the first period data only and 14 gave no information at all on what they had done. Twenty-eight meta-analyses had both crossover (n = 137, sample size n = 7,162) and parallel arm (n = 132, sample size n = 11,398) trials. Effect sizes correlated well with the two types of designs (rho = 0.72). Differences on whether the summary effect had a P < 0.05 or not were common due to limited sample sizes. The summary relative odds ratio for parallel arm vs crossover designs for favourable outcomes was 0.87 (95% CI, 0.74-1.02).<h4>Conclusions</h4>Crossover designs may contribute evidence in a fifth of systematic reviews, but few meta-analyses make use of their full data. The results of crossover trials tend to agree with those of parallel arm trials, although there was a trend for more conservative treatment effect estimates in parallel arm trials.","journal":"International Journal of Epidemiology","year":2007,"id":8882,"datarank":0.5709993734655481,"base_score":3.8066624897703196,"endowment":3.8066624897703196,"self_citation_contribution":0.5709993734655481,"citation_network_contribution":0.0,"self_endowment_contribution":0.5709993734655481,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":44,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.0474,"is_data_producer":false,"deposit_databanks":null,"is_oa":false,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2007-02-14","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":11861,"name":"Thomas A. Trikalinos","orcid":"0000-0002-3990-1848","position":1,"is_corresponding":false},{"id":148,"name":"John P. A. Ioannidis","orcid":"0000-0003-3118-6859","position":4,"is_corresponding":false},{"id":76032,"name":"Dimitrios N Lathyris","orcid":null,"position":0,"is_corresponding":true}],"reference_count":49,"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":[]}