Methods

Quasi-experiment

A quasi-experiment evaluates an intervention or change without random assignment to the relevant conditions. Researchers may compare existing groups, examine change before and after an intervention, or use a time series. These designs can inform causal questions when the comparison and assumptions are defensible. Simply collecting a before-and-after score does not identify the intervention’s effect.

Did introducing a new tutoring program improve performance beyond changes that would otherwise have occurred?

How it works

  1. In a synthetic school project, identify when the program started and how eligibility or access was decided. Describe the comparison group rather than calling it equivalent by assumption. Establish what outcome was measured before the program and whether the same measurement can be used afterward.
  2. Collect repeated outcomes when feasible and document other changes during the period. Consider whether the groups were already moving differently before the program began. Record differences in teachers, assessment timing and participation that could offer explanations besides the tutoring itself.
  3. Compare the observed change with the best available account of what would have happened without the program. State the assumptions supporting that comparison. Examine whether a concurrent policy, maturation, selection or regression toward typical scores could explain the result, and keep causal wording proportional to that evidence.

Evidence: (Research Methods in Psychology: Quasi-Experimental Research, n.d.)

Tutoring introduced in an existing class

Teaching scenario

This teaching scenario imagines a school offering tutoring to one existing class while another continues its usual instruction. Neither outcomes nor benefits are claimed. If the tutored class improved more, teacher differences or different starting trajectories might still matter. A pretest can reveal some initial differences but cannot establish that every relevant difference has been removed.

This example is constructed for learning. It does not report an observed research result.

What can you conclude?

Evaluate changes in settings where random assignment is unavailable and build a causal argument with explicit design-specific assumptions.

Evidence: (Research Methods in Psychology: Quasi-Experimental Research, n.d.)

Limits and common mistakes

  • Selection into conditions and unmeasured group differences can threaten the comparison.
  • Events occurring alongside the intervention can mimic its effect, especially with only one pretest and posttest.

A mistake to catch

Calling the comparison group equivalent because its starting average was similar, or attributing any post-intervention improvement to the intervention.

Evidence: (Research Methods in Psychology: Quasi-Experimental Research, 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: Quasi-experimental research. (n.d.). https://opentextbc.ca/researchmethods/chapter/quasi-experimental-research/

    Quasi-experiment: summary, procedure rationale, allows, limits and pitfall; nonequivalent groups, pretest-posttest and interrupted time-series logic Open teaching chapter by the textbook authors, read 21 October 2026. Not a primary empirical study.

Keep reading

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

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

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

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