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Relative validity of a food frequency questionnaire supported by images

Abstract

The scope of this study was to evaluate the relative validity of a food frequency questionnaire (FFQ) designed for adolescents. The study involved a sample of 106 adolescents (57% girls) aged between 11 and 18. The FFQ was administered in one-on-one interviews with the support of the 93 photographs of food items. Overall averages of energy and nutrient intake of three 24-hour recalls (24h-R) were used as benchmarks. They were then compared with those estimated from the FFQ using the Spearman correlation coefficient, weighted kappa for the agreement between classifications into quartiles and Bland-Altman limits of agreement. The correlation coefficients ranged from 0.27 to 0.49 (mean = 0.43), the weighted kappa ranged from 0.28 to 0.51 (mean = 0.40), and the estimated Bland-Altman mean limits of agreement ranged from 109 to 159% (mean = 130%). Approximately 30% of the estimates were classified into the same quartile while about 90% were categorized into the same or adjacent quartiles. Supporting the application of the FFQ with photographs provided more favorable results than those observed for the questionnaire alone. The FFQ was considered appropriate to categorize adolescents according to gradients of dietary intake.

Food consumption; Questionnaire; Photographs; Adolescents; Validity

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