Validation of the Rational-Experiential Inventory (REI-40) in Brazilian Portuguese

(1) Background: The Rational-Experiential Inventory (REI-40) is a widely used instrument for assessing individual differences in rational and experiential thinking styles based on Cognitive-Experiential Self-Theory (CEST). Despite its international prominence, no comprehensive validation existed for Brazilian Portuguese populations. (2) Methods: This study validated the REI-40 for Brazilian Portuguese through confirmatory factor analysis (CFA) estimated with a robust weighted least squares estimator (WLSMV) appropriate for ordinal items, comparison of competing structural models, internal-consistency and validity testing, and tests of measurement invariance across sex, education, and age, in a sample of 464 legal professionals from Brazil’s Advocacy-General of the Union. (3) Results: The hypothesized four-factor, 40-item model showed acceptable fit (χ2(734) = 1815.8, CFI = 0.902, TLI = 0.896, RMSEA = 0.056, SRMR = 0.080) and clearly outperformed unidimensional and two-factor alternatives. McDonald’s omega indicated good internal consistency for all subscales (ω = 0.79–0.87). Measurement invariance across sex, education, and age was supported at the configural and metric levels. Validity evidence included positive correlations between rational subscales and CRT-7 (r = 0.24–0.31) and weak or negative correlations for experiential subscales. (4) Conclusions: The Brazilian Portuguese REI-40 demonstrates adequate psychometric properties for measuring thinking styles in professional populations.