The principle of parallelism in the design of studies to estimate treatment effects.

  title={The principle of parallelism in the design of studies to estimate treatment effects.},
  author={Charles S. Reichardt},
  journal={Psychological methods},
  volume={11 1},
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… CONTINUE READING

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