Relative validity of a food-frequency questionnaire developed to assess food intake of schoolchildren living in the Brazilian Western Amazon.

This study aimed to assess the relative validity of a food frequency questionnaire (FFQ) developed to assess food intake of schoolchildren from the Brazilian Western Amazon. The dietary intakes of 61 schoolchildren, aged between six and nine 9 years, were measured using two 24-hour dietary recalls and one FFQ, conducted with the children's, mother or guardians. Validity of the FFQ compared to the mean of the two dietary recalls was assessed using Pearson's correlation coefficient adjusted for attenuation and energy intake, Bland & Altman plots and evaluation of agreement levels between the two assessment methods. Energy-adjusted and deattenuated correlation coefficients ranged from -0.03 for vitamin C, to 0.93 for calcium. The mean coefficient was 0.46. The mean proportion of subjects classified within one quintile by the two methods was 66%. The Bland & Altman plots indicated good agreement for almost all nutrients, with a mean limit of agreement of 108%. These results indicate that, although there was a lack of accuracy for certain nutrients, such as vitamins A and C, the FFQ ensures reliable estimates of intake of most nutrients.