Objective: To develop a psychometrically valid questionnaire for testing knowledge on micronutrients and to assess the relationship between knowledge and biomarkers of micronutrient status among adolescents.
Design: Cross-sectional, institution-based, validity and reliability study.
Setting: Seven higher secondary schools were covered in the limits of Greater Hyderabad Municipal Corporation, Hyderabad, India.
Subjects: Students aged 15-19 years, n 92 for the pre-test, n 108 for test-retest and n 109 for studying the relationship between knowledge and biomarkers of Fe, retinol, ascorbic acid, α-tocopherol, folic acid and vitamin B12 status.
Results: From an item pool of 106, thirty-one items were selected based on content validity. Statistical tools to obtain a valid and reliable questionnaire among adolescent boys and girls resulted in eighteen items with a difficulty index of 0·11-0·86, discrimination index of 0·20-0·72 and validity index (point bi-serial correlation) of 0·10-0·62. Reliability as measured by Cronbach's α was 0·71 and the intra-class correlation coefficient was 0·80. A Bland-Altman plot showed good agreement between test and retest scores. The mean response score to the eighteen-item questionnaire was 5·2 (sd 2·68). The mean values of serum retinol were significantly different (P = 0·022) between groups below (24·8 (sd 6·64) μg/dl) and above (28·0 (sd 7·67) μg/dl) the 50th percentile of knowledge score. The relationship persisted after controlling for economic status as a covariate using analysis of covariance (P = 0·018). Other micronutrients did not show any significant relationship.
Conclusions: A valid and reliable eighteen-item knowledge questionnaire was constructed and found to have a significant positive relationship with plasma retinol status alone.