Psychometric validation of the French version of two scales measuring general (HLS19-Q12) and navigational (HLS19-NAV) health literacy using the Rasch model

Abstract

Background: To examine the psychometrics properties of the French version of two scales measuring general (HLS19-Q12) and navigational (HLS19-NAV) health literacy (HL) using two validation methods based on modern psychometric test theories: a Rasch model analysis and structural equation models (SEM). Methods: The data on representative samples of the French adult population came from the Health Literacy Survey (N=2 003), conducted in France in two waves (2020 and 2021), and from the third wave of SLAVACO study (N=2 022), conducted in December 2021. A Rasch analysis was performed using a partial credit model adapted to polytomous data. Category probability curves were used to examine whether participants found it consistently difficult to distinguish between response options. A Person Separation Index (PSI) of 0.7 has conventionally been considered to be the minimum acceptable PSI level. Chi-square fit statistics, expressed as infit and outfit mean square statistics, were calculated for each item in the two scales. An acceptable fit corresponded to average values between 0.7 and 1.3. Differential item functioning (DIF) was also examined for each item in the two scales as a function of age, gender, and economic status. The goodness of fit of the SEM was assessed using the following indices: SRMR≤0.08; RMSEA≤0.08; CFI and TLI, good fit if close to 1. Results: The Rasch analysis demonstrated the unidimensionality of the French version of the scales measuring general and navigational HL. The PSI values for both scales were greater than 0.90. No disordered categories were observed. No evidence of significant DIF was found when associated with gender and economic status. However, two items for both scales had a DIF which was dependent on age. SEM indices showed adequate goodness of fit with strong significant correlation between the two latent traits. Conclusions: Our results, based on a rigorous statistical analysis, verified the psychometric parameters of the French version of the HLS19-Q12 and HLS19-NAV scales. Despite strong correlation between both scales, each measured a different latent trait. Moreover, despite the fact that presence of DIF was weak, attention must nonetheless be paid when comparing scale response scores between young and older respondents.