Methods

Within-subjects design

The same participants complete each condition of a comparison. This allows the researcher to compare a person with that person under another condition, reducing some variation arising from stable individual differences. In an experiment, condition order needs deliberate control. Repeated measurement alone does not make a study experimental, and not every manipulation can be reversed or repeated meaningfully.

Does the same participant perform differently with two versions of a task?

How it works

  1. For a synthetic modern task comparison, define the two conditions and use comparable materials. Decide whether experiencing the first task could permanently change the second. If the first condition teaches a skill that cannot be unlearned, reconsider whether a within-subjects comparison answers the intended question.
  2. Allocate participants to planned condition orders, using random assignment to order where appropriate. Balance which condition occurs first and include breaks when useful. Keep a record of the order actually completed, rather than assuming the scheduling plan was followed without exception.
  3. Compare paired outcomes with an analysis that respects their dependence. Inspect order patterns, errors and missing sessions alongside the primary outcome. Ask whether practice, fatigue, context or lingering effects could account for a difference. Counterbalancing helps address order effects but cannot erase an irreversible treatment effect.

Evidence: (Research Methods in Psychology: Experimental Design, n.d.); (Stroop (1935): Studies of Interference in Serial Verbal Reactions, n.d.)

Stroop’s color-naming comparison

Published study

In Experiment 2 of his 1935 paper, Stroop had participants name the colors of solid squares and the ink colors of conflicting color words. The same participants completed both kinds of test. The paper describes opposite test sequences for the two halves of the sample to address practice and fatigue. This is a documented historical example, not a claim that every modern Stroop task uses the same materials or ordering scheme.

Evidence: (Stroop (1935): Studies of Interference in Serial Verbal Reactions, n.d.)

What can you conclude?

Estimate a condition difference using comparisons within participants while accounting for stable person-level differences.

Evidence: (Research Methods in Psychology: Experimental Design, n.d.); (Stroop (1935): Studies of Interference in Serial Verbal Reactions, n.d.)

Limits and common mistakes

  • Practice, fatigue, context and carryover can confound a condition with its position in the sequence.
  • Some interventions have lasting effects or expose the hypothesis, making repeated conditions unsuitable.

A mistake to catch

Giving everyone condition A first and condition B second, then attributing the entire difference to the condition.

Evidence: (Research Methods in Psychology: Experimental Design, n.d.); (Stroop (1935): Studies of Interference in Serial Verbal Reactions, n.d.)

Sources and inspection notes

Links checked October 21, 2026. Inspection scope is stated for each source; an access date is not a publication date.

  1. Research methods in psychology: Experimental design. (n.d.). https://opentextbc.ca/researchmethods/chapter/experimental-design/

    Randomized experiment: procedure 2 and pitfall (sampling versus assignment). Within-subjects: summary, procedure, allows, limits, pitfall (carryover and counterbalancing) Open teaching chapter by the textbook authors, read 21 October 2026. Not a primary empirical study.

  2. Stroop (1935): Studies of interference in serial verbal reactions. (n.d.). https://www.yorku.ca/pclassic/Stroop/

    Within-subjects design: published example only; Experiment 2 materials and alternating test orders Primary paper in an openly accessible scholarly transcription at York University, Experiment 2 read 21 October 2026. DOI 10.1037/h0054651. Historical procedures are described, not recommended as a current reporting template.

Keep reading

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020). Psychology 2e. OpenStax. https://openstax.org/books/psychology-2e/pages/2-3-analyzing-findings

Nearest related OpenStax Psychology 2e reading. This is a course connection, not evidence for every specialist detail above.

Specialist reading: Research methods in psychology: Experimental design. (n.d.). https://opentextbc.ca/researchmethods/chapter/experimental-design/

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