title: [When is enough evidence available?; interim analyses in clinical trials].
abstract: There are ethical and economic reasons to design and conduct medical research as efficiently as possible. Clinical trials often take a long time because of the number of patients that must be included and the follow-up time in the study. Many data already become available during that time. By making interim analyses of these data it is possible to decide whether a final conclusion can be made. This may save time and may lead to a reduction in the number of patients. The statistical methodology of interim analyses is more complex than a fixed sample analysis and must be planned carefully in advance. The most important methods are sequential analysis and group sequential analysis. Both methods are aimed at a low risk of a false-positive conclusion. In this article we explain the application of these methods as well as considerations in the design of a study and interpretation of the results.
authors.affiliation: UMC Utrecht, Julius Centrum voor Gezondheidswetenschappen en Eerstelijns Geneeskunde, afd. Biostatistiek & Research Support, Utrecht, the Netherlands. i.vandertweel@umcutrecht.nl
authors.forename: Ingeborg van
authors.initials: Iv
authors.lastname: van der Tweel
authors.forename: Kit C B
authors.initials: KC
authors.lastname: Roes
mesh_terms: D035843:Biomedical Research / Q000191:economics / Q000592:standards*; D002986:Clinical Trials as Topic; D003362:Cost-Benefit Analysis; D003627:Data Interpretation, Statistical; D019317:Evidence-Based Medicine; D006801:Humans; D015233:Models, Statistical; D010934:Planning Techniques; D012107:Research Design