Validation of the Finnish extra short five 30-item personality scale in a nationally representative sample

This study investigated validity of the Finnish version of the Extra Short Five self-report questionnaire (XS5), a short, 30-item scale measuring personality according to the Five Factor Model (FFM). It utilized a nationally representative sample of 1007 Finnish adults. We evaluated structural validity, internal consistency reliability, convergent and discriminant validity, and criterion-related validity. We also examined the presence of response bias and measurement invariance. Using conventional cut-offs (CFI ≥ 0.90, RMSEA≤0.08, SRMR≤0.08), the scale demonstrated marginal fit (CFI = 0.84; RMSEA = 0.08; SRMR = 0.08) with moderate internal consistency across dimensions (McDonald's ω: N = 0.80, E = 0.72, C = 0.69, O = 0.65, A = 0.60; only Neuroticism exceeded the 0.70 threshold). Controlling for response bias with a hierarchical second-order bifactor model yielded substantially improved fit (ΔCFI = +0.06, ΔRMSEA -0.01; CFI = 0.90, GFI = 0.96, RMSEA = 0.07, SRMR = 0.07), confirmed as superior to an orthogonal bifactor parameterisation (CFI = 0.64). Multi-group CFA provided partial evidence of invariance across sex, age, region, and education level, with items e5 (Activity) and o4 (Ideas) primarily driving gender scalar non-invariance and item e4 (Excitement-Seeking) region metric non-invariance. Convergent validity was found for Neuroticism-negative valence (r = 0.09, p < .01) and Extraversion-positive valence (r = 0.09, p < .01), though these correlations are small. Criterion-related validity was confirmed via associations with educational attainment and household income. The Finnish XS5 is a viable short measure of personality where time is constrained and domain-level scores are sufficient, with caution recommended for mean comparisons across gender and region.