Related Experiment Video
Updated: Aug 9, 2026

A Within-Subject Experimental Design using an Object Location Task in Rats
Published on: May 6, 2021
The principle of parallelism in the design of studies to estimate treatment effects
1University of Denver, Denver, CO 80208, USA. creichar@du.edu
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.
Related Concept Videos
Bioequivalence Experimental Study Designs: Repeated Measures, Cross-Over, Carry-Over, and Latin Square Designs
Crossover Experiments
Crossover designs are performed even with smaller sample sizes since the samples can act as their controls. These are better than simple randomized trials since patients are exposed to all the treatments.
Study Designs in Epidemiology
Observational studies are those where the researcher does not intervene but rather observes natural variations. They include cross-sectional, cohort, and case-control studies.
Group Design
Study Design in Statistics
Does aspirin reduce the risk of heart attacks? Is one brand of fertilizer more effective at growing roses than another? Is fatigue as dangerous to a driver as the influence of alcohol? Questions like these are answered using randomized experiments with proper...
Bioequivalence Experimental Study Designs: Completely Randomized and Randomized Block Designs

