Comparison of Self-Administered Web-Based and Interviewer Printed Food Frequency Questionnaires for Dietary...

Innovative tools for assessing food and nutrient intakes in adolescence are essential to uncover the long-term effects of diet on chronic diseases. Here, we developed and compared a web-based self-administered food frequency questionnaire (web-FFQ) with a traditional interviewer printed FFQ (print-FFQ) among 174 Italian adolescents (aged 15-18 years). To assess the reliability of the web-FFQ compared with the print-FFQ, we used Spearman's rank correlation coefficients, Wilcoxon rank test, quartile misclassification analysis, Cohen's weighted kappa and the Bland-Altman method. Correlation coefficients ranged from 0.14 (i.e., pizza) to 0.67 (i.e., raw vegetables) for foods, and from 0.45 (i.e., monounsaturated fatty acids, MUFA) to 0.62 (i.e., zinc) for nutrients. Results from the Wilcoxon rank test showed that food and nutrient intakes were comparable between two FFQs, except for nuts, shellfish, fruit juices and MUFA. Adolescents classified into the same or adjacent quartiles ranged from 68.2% (i.e., tea) to 89.1% (i.e., raw vegetables and dipping sauces) for foods, and from 77.2% (i.e., vitamin C) to 87.2% (i.e., folate and calcium) for nutrients. Except for pizza, the weighted kappa indicated moderate to substantial agreement for other foods and nutrients. Finally, we demonstrated that the web-FFQ significantly overestimated shellfish and fruit juice intakes, while it underestimated nuts, canned fish, olive oil, total energy intake, fatty acids and calcium. The limits of agreement analysis indicated moderate to wide individual differences for all groups. In conclusion, our self-administered web-FFQ represents an easy, suitable and cost-effective tool for assessing food and nutrient intakes in adolescents. However, the wide individual differences in level of agreement suggest that additional refinements and calibrations are necessary to investigate the effects of absolute nutrient intakes at the individual level.