title: Relative validity and reproducibility of a quantitative food frequency questionnaire for adolescents with type 1 diabetes: validity of a food frequency questionnaire.
abstract: Background. Food frequency questionnaires are used to assess dietary intake in epidemiological studies. Objective. The aim of the study was to assess the relative validity and reproducibility of a quantitative food frequency questionnaire (QFFQ) for adolescents with type 1 diabetes.
  
  
  METHODS
  Validity was evaluated by comparing the data generated by QFFQs to those of 24-hour recalls (24 hrs). QFFQs were applied twice per patient to assess reproducibility. Statistical analysis included performing t-tests, obtaining Pearson correlation coefficients when necessary, correcting measurements for randomness by the weighted kappa method, calculating intraclass correlation coefficients, and generating Bland-Altman plots (P < 0,05). Results. The total energy and nutrient intake as estimated by the QFFQs were significantly higher than those from 24 hrs. Pearson correlation coefficients for energy-adjusted, deattenuated data ranged from 0.32 (protein) to 0.75 (lipid, unsaturated fat and calcium). Weighted kappa values ranged from 0.15 (vitamin C) to 0.45 (calcium). Bland-Altman plots indicated acceptable validity. As for reproducibility, intraclass correlation coefficients ranged from 0.24 (calcium) to 0.65 (lipid), and the Bland-Altman plots showed good agreement between the two questionnaires.
  
  
  CONCLUSIONS
  The QFFQ presented an acceptable ability to classify correctly and with good reproducibility, adolescents with type 1 diabetes according to their levels of dietary intake.
authors.affiliation: Faculdade de Nutrição, Universidade Federal de Goiás, Rua 227, Quadra 68 s/n, Setor Leste Universitário, 74605-080 Goiânia, GO, Brazil.
authors.forename: Rosana de Moraes Borges
authors.initials: Rde M
authors.lastname: Marques
authors.affiliation: Faculdade de Nutrição, Universidade Federal de Goiás, Rua 227, Quadra 68 s/n, Setor Leste Universitário, 74605-080 Goiânia, GO, Brazil.
authors.forename: Amanda Cristine
authors.initials: AC
authors.lastname: de Oliveira
authors.affiliation: Faculdade de Nutrição, Universidade Federal de Goiás, Rua 227, Quadra 68 s/n, Setor Leste Universitário, 74605-080 Goiânia, GO, Brazil.
authors.forename: Sheylle Almeida da Silva
authors.initials: SA
authors.lastname: Teles
authors.affiliation: Faculdade de Nutrição, Universidade Federal de Goiás, Rua 227, Quadra 68 s/n, Setor Leste Universitário, 74605-080 Goiânia, GO, Brazil.
authors.forename: Maria Luiza Ferreira
authors.initials: ML
authors.lastname: Stringuini
authors.affiliation: Faculdade de Nutrição, Universidade Federal de Goiás, Rua 227, Quadra 68 s/n, Setor Leste Universitário, 74605-080 Goiânia, GO, Brazil.
authors.forename: Nélida Shimid
authors.initials: NS
authors.lastname: Fornés
authors.affiliation: Hospital ENCORE, Rua Gurupi, Quadra 25 lt-6, Vila Brasília, 74905-350 Aparecida de Goiânia, GO, Brazil ; Centro de Estudos Avançados e Formação Integrada, Rua T-28, No. 1806, Setor Bueno, 74215-040 Goiânia, GO, Brazil ; Hospital e Maternidade São Cristóvão, Rua Américo Ventura, No. 123, Mooca, 03128-020 São Paulo, SP, Brazil.
authors.forename: Giulliano
authors.identifier: 0000-0002-8763-561X
authors.initials: G
authors.lastname: Gardenghi