Rational-Experiential Inventory-8 (REI-8): Development and Psychometric Evaluation of a Very Brief REI Version Using Ant Colony Optimization

Rational and experiential thinking styles are dispositional tendencies to approach the world in specific ways. The most commonly used instrument for assessing them is the Rational–Experiential Inventory-40 (REI-40), but its length may be impractical in time-constrained settings. Using ant colony optimization (ACO) we created and validated a very brief yet psychometrically sound version of REI.In study 1, with 813 Serbian participants (68% women, M age = 20), the ACO procedure produced the REI-8, comprising four items per Rationality and Experientiality scale. The very brief scales demonstrated good reliability and structural validity, correlated highly with the full-length scales, and remained mutually uncorrelated. Study 2 extended these findings in an independent Serbian sample (N = 283, 80% women, M age= 21). The two-factor model again showed good fit, preserving the theoretical independence of Rationality and Experientiality. Both scales again demonstrated good reliability and meaningful correlations with external variables.Taken together, our results support the conclusion that the REI-8 retains the core structure of the original version while using only a fraction of its length. It is a reliable, structurally sound, and externally valid instrument that can be efficiently used in future research.