Psychometric properties of a new functional health literacy questionnaire in Portuguese adolescents

BACKGROUND: Health literacy is associated with health behaviours. There is a lack of suitable instruments for assessing this determinant of health in adolescents. The Newest Vital Sign for the Portuguese adolescents (NVS-PTeen) is the only tool available; however, it was adapted from the original version and has some cultural constraints. We developed the Functional Literacy Questionnaire (FLiQ), the first scale to assess functional health literacy in adolescents using the information on a food label according to the European Union Regulation. This study aimed to assess classic psychometric properties of the FLiQ, in comparison to NVS-PTeen, among Portuguese adolescents. METHODS: We conducted a longitudinal observational study with three phases: (1) characterisation of the scale's content validity (Delphi panel with a group of experts; data collected through online forms); (2) self-administration of FLiQ and NVS-PTeen to adolescents enrolled in 7th to 9th grade (online or paper format); and (3) retest of FLiQ to the same group of subjects, after four weeks. RESULTS: FLiQ's overall content validity was excellent (average-content validity index=.95). A total of 372 adolescents (50.3% girls) aged between 12-17 years (median age: 13) participated in the study. Of these, 150 completed the test-retest assessment. Internal reliability was good (Kuder-Richardson-20=.70; 95% confidence interval (CI) .66-.75), as well as temporal reliability (intraclass correlation coefficient=.82; 95%CI .76-.87). FLiQ total score was correlated with the school year (rho=.17), and with Portuguese (rho=.35) and Maths grades (rho=.33). Exploratory factor analysis showed that FLiQ is composed by two dimensions (verbal and numeric competencies). CONCLUSIONS: FLiQ is a valid and reliable scale to measure functional health literacy among Portuguese adolescents. It can be used to monitor the literacy levels over time. KEY MESSAGES: • FLiQ is the first scale for measuring health literacy using the information on a food label according to the European Union Regulation No 1169/2011. • Health literacy is pivotal to public health promotion. The results suggest that this scale is suitable for monitoring and assessing public health promotion among adolescents.