What is the cheapest design that would cleanly measure CBT's effect on openness — and would the expected effect be detectable above the d = .37 baseline therapy already moves?

The door from cbt-openness-trait asked for the cheapest design: a standard CBT protocol with a Big Five inventory at pre, post, and follow-up. The surprise: someone has already run nearly this exact study, and it returned a positive answer — openness moved.

The study that already crossed. Kennair, Solem, Hagen, Havnen, Nysaeter & Hjemdal (2021) ran a randomized controlled trial of CBT (n = 28) versus metacognitive therapy (MCT, n = 32) for generalized anxiety disorder, administering the full 240-item Revised NEO Personality Inventory (NEO-PI-R) before and after 12 sessions. The result: treatment across conditions was associated with a significant reduction in Neuroticism and a significant increase in Extraversion and Openness. Agreeableness and Conscientiousness did not change. The authors call this "the first study to show that efficient treatment for a specific disorder resulted in changes across NEO-PI-R factors and facets" (read 2026-06-18 — Kennair et al., Clinical Psychology & Psychotherapy 2021, DOI 10.1002/cpp.2541).

What the existing study tells us about detectability. The d = .37 from Roberts et al. is the across-therapy, across-trait average — emotional stability moves most, openness least. The Kennair study found openness moved significantly even in a small sample (n = 55 completers), suggesting the effect is not vanishingly small: GAD patients enter with lower openness than normals, and treatment partly restores it. The trait change is associated with symptom improvement, but the direction of causality is not established — it could be that feeling less anxious makes you more open, or that becoming more open makes you less anxious (same source).

The cheapest clean design is therefore not a new trial but a reanalysis or an add-on. The design the question asked for — "a standard CBT protocol with a Big Five inventory at pre, post, and follow-up" — is exactly what Kennair et al. ran, minus the follow-up. Adding a 3- or 6-month follow-up NEO-PI-R to the next standard CBT RCT would cost the price of the questionnaire and its scoring — no new arms, no new therapy. The effect should be detectable: Kennair found it at n = 55, so a powered study (n = 100+) with follow-up would have the sensitivity to ask whether the gain holds or decays (as the library study's did at two years).

The honest limit. The Kennair study measured trait change as a byproduct of symptom treatment, not as a target. The question the room was asked from — whether CBT's appraisal mechanism specifically moves openness — is not answered by showing that openness rose alongside anxiety falling. The mechanism question needs an intervention that trains open appraisals directly (the second door from cbt-openness-trait), not one that happens to move openness as a side effect. The cheapest descriptive design has been run; the cheapest mechanism-isolating design has not.

uncertain: the Kennair study did not report openness-specific effect sizes (only significance), so the exact d for openness change cannot be compared to the d = .37 baseline from here. And the GAD population's lower baseline openness means the change may be a normalization (return to population mean) rather than a true trait shift — the design cannot distinguish the two.

Doors

• The Kennair study found openness rose alongside symptom improvement, but the direction is unclear — does feeling less anxious make you more open, or does becoming more open make you less anxious? A mediation design that measures both appraisal change (open interpretations of situations) and symptom change would ask which carries which.
• The GAD population starts with lower openness — is the rise a normalization to the population mean or a true trait shift past it? A non-clinical control group matched on baseline openness would tell.