title: Factorial experiments: efficient tools for evaluation of intervention components.
abstract: BACKGROUND
  An understanding of the individual and combined effects of a set of intervention components is important for moving the science of preventive medicine interventions forward. This understanding can often be achieved in an efficient and economical way via a factorial experiment, in which two or more independent variables are manipulated. The factorial experiment is a complement to the RCT; the two designs address different research questions.
  
  
  OBJECTIVE
  To offer an introduction to factorial experiments aimed at investigators trained primarily in the RCT.
  
  
  METHODS
  The factorial experiment is compared and contrasted with other experimental designs used commonly in intervention science to highlight where each is most efficient and appropriate.
  
  
  RESULTS
  Several points are made: factorial experiments make very efficient use of experimental subjects when the data are properly analyzed; a factorial experiment can have excellent statistical power even if it has relatively few subjects per experimental condition; and when conducting research to select components for inclusion in a multicomponent intervention, interactions should be studied rather than avoided.
  
  
  CONCLUSIONS
  Investigators in preventive medicine and related areas should begin considering factorial experiments alongside other approaches. Experimental designs should be chosen from a resource management perspective, which states that the best experimental design is the one that provides the greatest scientific benefit without exceeding available resources.
authors.affiliation: Department of Human Development and Family Studies; The Methodology Center. Electronic address: lmcollins@psu.edu.
authors.forename: Linda M
authors.initials: LM
authors.lastname: Collins
authors.affiliation: The Methodology Center.
authors.forename: John J
authors.initials: JJ
authors.lastname: Dziak
authors.affiliation: The Methodology Center.
authors.forename: Kari C
authors.initials: KC
authors.lastname: Kugler
authors.affiliation: The Methodology Center; Department of Statistics, Pennsylvania State University, University Park, Pennsylvania.
authors.forename: Jessica B
authors.initials: JB
authors.lastname: Trail
mesh_terms: D006801:Humans; D011314:Preventive Health Services / Q000379:methods*; D011315:Preventive Medicine / Q000379:methods; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D012107:Research Design
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