Social-Psychology Textbook Audit: External Validity

Every social psychology textbook emphasizes the problem of naturalistic studies (correlational research) that it is difficult to demonstrate cause-effect relationships in these studies.

Social psychology has a proud tradition of addressing this problem with laboratory experiments. The advantage of laboratory experiments is that they make it easy to demonstrate causality. The disadvantage is that laboratory experiments have low ecological validity. It is therefore important to demonstrate that findings from laboratory experiments generalize to real world behavior.

Myers and Twenge’s (2019) textbook (13e edition) addresses this issue in a section called “Generalizing from Laboratory to Life”

What people saw in everyday life suggested correlational research, which led to experimental research. Network and government policymakers, those with the power to make changes, are now aware of the results. In many areas, including studies of helping, leadership style, depression, and self-efficacy, effects found in the lab have been mirrored by effects in the field, especially when the laboratory effects have been large (Mitchell, 2012).

Mitchell, G. (2012). Revisiting truth or triviality: The external validity of research in the psychological laboratory. Perspectives on Psychological Science, 7, 109–117.

Curious about the evidence, I examined Mitchell’s article. I didn’t need to read beyond the abstract to see that the textbook misrepresented Mitchell’s findings.

Using 217 lab-field comparisons from 82 meta-analyses found that the external validity of laboratory research differed considerably by psychological subfield, research topic, and effect size. Laboratory results from industrial-organizational psychology most reliably predicted field results, effects found in social psychology laboratories most frequently changed signs in the field (from positive to negative or vice versa), and large laboratory effects were more reliably replicated in the field than medium and small laboratory effects.

Mitchell, G. (2012). Revisiting Truth or Triviality: The External Validity of Research in the Psychological Laboratory. Perspectives on Psychological Science7(2), 109–117.

So, a course in social psychology covers 80% results based on laboratory experiments that may not generalize to the real world. In addition, students are given the false information that these results do generalize to the real world, when evidence of ecological validity is often missing. On top of this, many articles based on laboratory experiments report inflated effect sizes due to selection for significance and the results may not even replicate in other laboratory contexts.

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