Improving measurement in nutrition literacy research using Rasch modelling: examining construct validity of stage-specific 'critical nutrition literacy' scales.

OBJECTIVE Critical nutrition literacy (CNL), as an increasingly important area in public health nutrition, can be defined as the ability to critically analyse nutrition information, increase awareness and participate in action to address barriers to healthy eating behaviours. Far too little attention has been paid to establishing valid instruments for measuring CNL. The aim of the present study was to assess the appropriateness of utilizing the latent scales of a newly developed instrument assessing nursing students' 'engagement in dietary habits' (the 'engagement' scale) and their level of 'taking a critical stance towards nutrition claims and their sources' (the 'claims' scale). DESIGN Data were gathered by distributing a nineteen-item paper-and-pencil self-report questionnaire to university colleges offering nursing education. The study had a cross-sectional design using Rasch analysis. Data management and analysis were performed using the software packages RUMM2030 and SPSS version 20. SETTING School personnel handed out the questionnaires. SUBJECTS Four hundred and seventy-three students at ten university colleges across Norway responded (52% response rate). RESULTS Disordered thresholds were rescored, an under-discriminating item was discarded and one item showing uniform differential item functioning was split. The assumption of item locations being differentiated by stages was strengthened. The analyses demonstrated possible dimension violations of local independence in the 'claims' scale data and the 'engagement' scale could have been better targeted. CONCLUSIONS The study demonstrates the usefulness of Rasch analysis in assessing the psychometric properties of scales developed to measure CNL. Qualitative research designs could further improve our understanding of CNL scales.