title: The principle of parallelism in the design of studies to estimate treatment effects.
abstract: An effect is a function of a cause as well as of 4 other factors: recipient, setting, time, and outcome variable. The principle of parallelism states that if a design option exists for any 1 of these 4 factors, a parallel option exists for each of the others. For example, effects are often estimated by drawing a comparison across recipients who receive different treatments. The principle of parallelism implies that an effect can also be estimated by drawing a comparison across settings, times, or outcome variables. Typologies of methodological options are derived from the principle of parallelism. The typologies can help researchers recognize a broader set of options than they would otherwise and thereby improve the quality of research designs.
authors.affiliation: University of Denver, Denver, CO 80208, USA. creichar@du.edu
authors.forename: Charles S
authors.initials: CS
authors.lastname: Reichardt
mesh_terms: D000704:Analysis of Variance; D006801:Humans; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data*; D015397:Program Evaluation / Q000706:statistics & numerical data; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data*; D015203:Reproducibility of Results; D012107:Research Design / Q000706:statistics & numerical data*