[Reproducibility and relative validity of the Food Frequency Questionnaire used in the ELSA-Brasil]

This study evaluated the reproducibility and relative validity of the Food Frequency Questionnaire (FFQ) used in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil). Participants (n = 281) completed the FFQ and three food records on two occasions during a 12-month period. Energy and nutrient values from food records were disattenuated and log-transformed. Reproducibility and validity were assessed by the intra-class correlation coefficient (ICC). Agreement between the two methods was evaluated by classification in tertiles. In the evaluation of reproducibility, ICC estimated ranged from 0.55 to 0.83 for protein and vitamin E, respectively. On relative validity, ICC ranged from 0.20 to 0.72 for selenium and calcium, respectively. Exact and adjacent agreement between methods varied from 82.9% for vitamin E to 89% for lipids and calcium (mean 86%). Average disagreement was 13.6%. In conclusion, this FFQ showed satisfactory reliability for all nutrients and reasonable validity, especially for energy, macronutrients, calcium, potassium, and vitamins E and C.