What are the pros and cons of a within-subjects design?

Within-subjects designs have many potential threats to internal validity, but they are also very statistically powerful.


  • Only requires small samples
  • Statistically powerful
  • Removes the effects of individual differences on the outcomes


  • Internal validity threats reduce the likelihood of establishing a direct relationship between variables
  • Time-related effects, such as growth, can influence the outcomes
  • Carryover effects mean that the specific order of different treatments affect the outcomes