When is it legitimate to exclude patients' data from study results?

Investigators in clinical trials are faced with difficulty when patients are inappropriately randomised into a trial or when information on patients' eligibility for inclusion is not available at the time of randomisation. Can such patients be excluded from the analysis of the study's outcomes without biasing the measure of effect? Fergusson and colleagues (p 652) consider that it may be acceptable to exclude patients after randomisation when investigators made mistakes in implementing eligibility criteria or when patients never received the intervention. But patients randomised because of excessively broad inclusion criteria who prove not to have the target condition should not be excluded. They recommend that investigators should specify any foreseeable post randomisation exclusions and that an independent committee should make the decision about such exclusions.

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Relevant Article

Post-randomisation exclusions: the intention to treat principle and excluding patients from analysis

Dean Fergusson, Shawn D Aaron, Gordon Guyatt, and Paul Hébert
BMJ 2002 325: 652-654. [Extract] [Full Text] [PDF]