Structural Validation and Measurement Invariance of the HLS-Q12 Health Literacy Instrument in Finnish Adults: Comparing Traditional and Alignment Methods

Objectives To examine the internal structure, internal consistency, and measurement invariance of the HLS-Q12 across sociodemographic groups in Finnish adults, using traditional multi-group confirmatory factor analysis (MGCFA) and alignment optimization. Methods We analyzed data from 7,077 Finnish adults drawn from a nationally representative national sample (n = 4,003) and a regional sample from North Savo (n = 3,074). Analyses included confirmatory factor analysis, MGCFA, and alignment optimization with Monte Carlo evaluation. Invariance was examined across gender, age, education, and study samples. Results Reliability was high (α = 0.905 ω = 0.896) and unidimensional structure (CFI = 0.951, TLI = 0.935, RMSEA = 0.058). MGCFA supported scalar invariance for gender, education, and study samples. Alignment optimization exhibited acceptable non-invariance (2.8%–25% of parameters), primarily in intercepts. Women and individuals with higher education showed higher health literacy; young adults exhibited higher levels than older cohorts. Conclusion The Finnish HLS-Q12 supported subgroup comparisons for population monitoring, with largely adequate measurement invariance across key sociodemographic groups. The evidence pertains primarily to internal structure and measurement invariance. Further studies should examine additional validity evidence using external criteria.