title: Reproducibility and relative validity of a food frequency questionnaire developed for female adolescents in Suihua, North China.
abstract: BACKGROUND
  This study aims to evaluate the reproducibility and validity of a food frequency questionnaire (FFQ) developed for female adolescents in the Suihua area of North China. The FFQ was evaluated against the average of 24-hour dietary recalls (24-HRs).
  
  
  RESULTS
  A total of 168 female adolescents aged 12 to 18 completed nine three consecutive 24-HRs (one three consecutive 24 HRs per month) and two FFQs over nine months. The reproducibility of the FFQ was estimated using intraclass correlation coefficients (ICCs), and its relative validity was assessed by comparing it with the 24-HRs. The mean values of the 24-HRs were lower than those of the FFQs, except for protein (in FFQ1) and iron (in FFQ2). The ICCs for all nutrients and food groups in FFQ1 and FFQ2 were moderately correlated (0.4-0.8). However, all the ICCs decreased after adjusting for energy. The weighted κ statistic showed moderate agreement (0.40-0.6) for all nutrients and food groups, except for niacin and calcium, which showed poor agreement (0.35). The relative validity results indicate that the crude Spearman's correlation coefficients of FFQ1 and the 24-HRs ranged from 0.41 (for Vitamin C) to 0.65 (for fruit). The coefficients of each nutrient and food group in FFQ2 and the 24-HRs were higher than those in FFQ1 and the 24-HRs, indicating good correlation. Although all energy-adjusted Spearman's correlation coefficients were lower than the crude coefficients, de-attenuation to correct for intra-individual variability improved the correlation coefficients. The weighted κ coefficients of nutrients and food groups ranged from 0.32 for beans to 0.52 for riboflavin in FFQ1 and the 24-HRs, and 0.32 for Vitamin C to 0.54 for riboflavin in FFQ2 and the 24-HRs.
  
  
  CONCLUSIONS
  The FFQ developed for female adolescents in the Suihua area is a reliable and valid instrument for ranking individuals within this study.
authors: Department of Children Health and Hygiene, School of Public Health, Harbin Medical University, Harbin, China.
authors: Wei
authors: W
authors: Xia
authors: Caihong
authors: C
authors: Sun
authors: Li
authors: L
authors: Zhang
authors: Xin
authors: X
authors: Zhang
authors: Jiajia
authors: J
authors: Wang
authors: Hui
authors: H
authors: Wang
authors: Lijie
authors: L
authors: Wu
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