[Assessment of reproducibility and validity of a food frequency questionnaire in a sample of adults living in Porto Alegre, Rio Grande do Sul State, Brazil].

The reproducibility and validity of a Food Frequency Questionnaire (FFQ) was evaluated in 83 adults living in a State capital in southern Brazil. The reproducibility and validity were tested with intra-class correlation coefficients (ICC). Mean nutrient intakes from three 24-hour dietary recalls (24hDR) were compared to mean intakes from each FFQ (FFQ1 and FFQ2), adjusted for energy intake and within-person variation. Nutrients were categorized into quartiles and assessed using weighted kappa statistics. Mean ICC for the test-retest FFQ ranged from 0.44 (95%CI: -0.19-0.76) to 0.83 (95%CI: 0.72-0.90) for energy-adjusted carbohydrate and vitamin C intakes, respectively. Mean ICC, energy-adjusted and corrected for within-person variability, ranged from 0.23 (95%CI: -0.22-0.61) to 0.86 (95%CI: 0.21-1.16) for vitamin A and lipids for the FFQ1, and 0.50 (95%CI: -0.16-0.91) to 0.95 (95%CI: 0.79-1.05) for vitamin A and energy for the FFQ2. For the FFQ1, calcium showed the lowest weighted kappa value (0.10; 95%CI: 0.00-0.26), while vitamin C (0.38; 95%CI: 0.23-0.53) and total energy (0.38; 95%CI: 0.24-0.52) had the highest weighted kappa for the FFQ2. The FFQ showed good reproducibility and reasonable relative validity.