Reproducibility and validity of a food frequency questionnaire in assessing dietary intakes of low-income Caucasian postpartum women living in Sheffield, United Kingdom

The aim of this study was to examine the reproducibility and validity of a semi-quantitative food frequency questionnaire (FFQ) for assessing dietary intakes of low-income, Caucasian, English-speaking, postpartum women living in Sheffield, United Kingdom. Data was obtained from a cross-sectional sample of the 'Healthy Start' study; a population-based survey of mothers and infants. Participants completed two FFQs at 4 and 8 weeks postpartum. Measures from 24-hour dietary recalls (24HDRs) were collected at 4, 6, 8 and 12 weeks postpartum. In the reproducibility study, crude Pearson's correlation coefficients ranged from 0.40 (riboflavin) to 0.73 (thiamine), mean value 0.54. In the validation study, crude Pearson correlation coefficients between the FFQ and the measures from the 24HDRs ranged from 0.10 (B12) to 0.55 (manganese), mean value 0.34. Energy-adjustments and corrections for attenuation had no significant effect on the strength of the correlation both observed in the reproducibility and validity study. On average, 68% of the participants were classified correctly, and 3% were misclassified into the extreme opposite quintile of the distribution. The authors conclude that the questionnaire performed well for the majority of nutrients examined and that is a valid tool for ranking individuals according to nutrient distribution.