Initial psychometric evaluation of the SER5: A forced-choice Big Five inventory scored with Thurstonian item response...

This study reports an initial psychometric evaluation of the SER5, a forced-choice Big Five inventory scored with Thurstonian item response theory (TIRT), and compares its trait estimates with a Likert-type comparison measure, the Big Five Personality Trait Short Questionnaire, in a Latin American personnel-selection context. A total of 6583 job applicants completed the SER5, presented as non-consequential, during real selection processes on an online recruitment platform used across Latin America. A confirmatory TIRT model supported the intended five-factor structure with good global fit; however, exploratory analyses (parallel analysis and the Maximal Kaiser Criterion) did not recover five dimensions, consistent with the rank-deficiency expected for the instrument's all-homopolar block design. Marginal reliability exceeded 0.70 for all factors except Emotional Stability (ρ = 0.62), and conditional precision varied markedly across the trait range. Discriminant validity was weak, with a mean absolute inter-trait correlation less favorable than that of every forced-choice inventory in a recent benchmark, consistent with a block-design limitation, although alternative designs were not compared. In a subsample of 714 complete cases, convergent correlations with the Likert comparison measure were modest, although TIRT scores converged significantly better than raw forced-choice scores for Extraversion and Agreeableness; for Openness, TIRT scoring only removed a negative raw-score association. Overall, forced-choice and Likert scores were not interchangeable: TIRT scoring appears necessary but not sufficient, block design is a plausible key constraint, and the SER5, designed as a supplementary screening tool, still requires criterion validation. Organizations should not transfer norms or cut-off scores across response formats.