Validity and reliability testing of a short questionnaire developed to assess consumers’ use, understanding and perception of food labels

Abstract

Food labels may have an important function in communicating nutrition information and have considerable potential to influence food choice and dietary behaviour. To assess the validity and reliability of a short (self-complete) questionnaire designed to measure consumers' use and understanding of food labels. Questionnaire content was determined by gaps highlighted in a literature review of food labelling. Nineteen questions (49 items) assessing frequency of label reading perceived importance of food labels, regularity of dining out, desire to have nutrition information at specific catering outlets and ability to perform nutrition information tasks were formulated and presented on four pages of A4. With the exception of two open-ended questions, all items were presented as closed (field box) structures. Content validity, face validity, item analysis, repeat and internal reliability were assessed. Nutrition experts (26) completed detailed content validity assessment, resulting in high scores for appropriateness, importance and phrasing of questions, although grammar and terminology changes were required. Face validity indicated that the questionnaire was quick to complete (<15 min), easy to follow and comprehensible. Cronbach's alpha scores (internal reliability) for questions with multiple sections ranged from 0.72 to 0.91, indicating good internal consistency. Repeat reliability testing showed Spearman's correlation coefficients ranging from 0.51 to 0.97 (all P<0.001) showing high temporal stability. Item Difficulty analysis indicated that questions (Section C only) were at an appropriate level (with P between 20 and 80% for all items). Item discrimination analysis ranged from r=0.43 to 0.70, highlighting that items were suitable for inclusion. This questionnaire is a suitable tool for assessing consumers' use, understanding and perception of food labels.