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For both randomization strategies, the maximum type I error rate increases with the effect size in the secondary endpoint and the correlation between endpoints. The maximum inflation increases with smaller block sizes if information on the block size is used in the reassessment rule. Based on our findings, we do not question the well‐established use of blinded sample size reassessment methods with nuisance parameter estimates computed from the blinded interim data of the primary endpoint. However, we demonstrate that the type I error rate control of these methods relies on the application of specific, binding, pre‐planned and fully algorithmic sample size reassessment rules and does not extend to general or unplanned sample size adjustments based on blinded data. © 2015 The Authors. <jats:italic>Statistics in Medicine</jats:italic> Published by John Wiley &amp; Sons Ltd.</jats:p>","journal":"Statistics in Medicine","year":2016,"id":590566,"datarank":0.536641357053262,"base_score":2.70805020110221,"endowment":2.70805020110221,"self_citation_contribution":0.40620753016533157,"citation_network_contribution":0.13043382688793037,"self_endowment_contribution":0.40620753016533157,"citer_contribution":0.13043382688793037,"corpus_percentile":null,"corpus_rank":null,"citation_count":14,"citer_count":6,"citers_with_citation_signal":4,"citers_with_endowment":4,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":null,"is_data_producer":false,"deposit_databanks":null,"is_oa":false,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":null,"fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":38095,"name":"Martin Posch","orcid":"0000-0001-8499-8573","position":1,"is_corresponding":false},{"id":1510995,"name":"Dominic Magirr","orcid":null,"position":2,"is_corresponding":false},{"id":925931,"name":"Magdalena Żebrowska","orcid":"0000-0003-0589-4173","position":0,"is_corresponding":false}],"reference_count":0,"raw_metadata":{"has_enrichment":true,"resolved":true,"title":"Maximum type I error rate inflation from sample size reassessment when investigators are blind to treatment labels","abstract":"<jats:p>Consider a parallel group trial for the comparison of an experimental treatment to a control, where the second‐stage sample size may depend on the blinded primary endpoint data as well as on additional blinded data from a secondary endpoint. 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