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The 2 × 2 factorial design: Its application to a randomized trial of aspirin and U.S. physicians
Author(s) -
Stampfer Meir J.,
Buring Julie E.,
Willett Walter,
Rosner Bernard,
Eberlein Kimberly,
Hennekens Charles H.
Publication year - 1985
Publication title -
statistics in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.996
H-Index - 183
eISSN - 1097-0258
pISSN - 0277-6715
DOI - 10.1002/sim.4780040202
Subject(s) - factorial experiment , randomized controlled trial , completely randomized design , research design , aspirin , test (biology) , statistics , medicine , clinical trial , factorial , scale (ratio) , computer science , mathematics , paleontology , physics , quantum mechanics , biology , mathematical analysis
The 2 × 2 factorial design calls for randomizing each participant to treatment A or B to address one question and further assignment at random within each group to treatment C or D to examine a second issue, permitting the simultaneous test of two different hypotheses. This design can increase the efficiency of large‐scale clinical trials. The Physicians' Health Study, a randomized trial of aspirin and beta‐carotene among U.S. physicians, illustrates some features and potential problems in the design and analysis of a factorial trial. The most common concern, interaction between treatments, is generally an advantage rather than a limitation of this design. Although such interactions are relatively uncommon, this design provides a means to measure an effect which otherwise might not be apparent. If the interaction is sufficiently severe, however, then loss of power is possible.