Reproducibility and Validity of a Food Frequency Questionnaire for Assessing Dietary Consumption via the Dietary Pattern Method in a Chinese Rural Population

Abstract

Objective: This study was conducted to assess the reproducibility and validity of a food frequency questionnaire (FFQ) that was developed to assess the overall dietary consumption via dietary pattern method in a rural population in southwest China.

Methods: A total of 179 participants aged between 40 and 70 years old were included in this study. Participants administered FFQ at baseline (FFQ1) and one year later (FFQ2) to assess the reproducibility. Six 3-day 24-hour recalls (24HRs) were completed between the administrations of two FFQs to determine the validity. Dietary patterns from three separate dietary sources were derived by using principle component factor analysis. Comparisons between dietary pattern scores were made by using Pearson or intraclass correlation coefficient, cross-classification analysis, weighted kappa (κ) statistic and Bland-Altman analysis. The de-attenuated method was adopted to correct the monthly and seasonally variation and the partial correlation analysis was used correct the influence by total energy intake.

Results: Two major dietary factors, labeled as prudent pattern and processed food pattern, were identified. The prudent pattern was characterized by higher factor loadings of wheat, rice, fresh vegetables, bean products, nuts, red meat, white meat and fresh eggs; and the processed food pattern was characterized by higher factor loadings of pickled vegetables, preserved vegetables and salted meat. Between Two FFQs, intraclass correlation coefficients were 0.57 for prudent pattern and 0.55 for processed food pattern, partial Pearson correlation coefficients were 0.51 for the prudent pattern and 0.56 for the processed food pattern; weighted κ statistic ranged from 0.45 (for the prudent pattern) to 0.56 (for the processed food pattern). Between FFQs and 24HRs, de-attenuated correlation coefficients ranged from 0.54 to 0.78 for the prudent pattern and from 0.55 to 0.61 for the processed food pattern; partial Pearson correlation coefficients ranged from 0.41 to 0.56 for the prudent pattern and from 0.42 to 0.44 for the processed food pattern; weighted κ statistic ranged from 0.42 to 0.46 for prudent pattern and from 0.43 to 0.60 for processed food pattern. The Bland-Altman plots and limits of agreement indicated that the deviation/divergence was not obvious for both of the patterns between FFQ1 and FFQ2 and between FFQs and 24HRs.

Conclusion: The study suggests that the FFQ is reasonably reproducible and valid to assess the overall dietary consumption via dietary pattern methods in the Chinese rural population.

Fig 1. Study design and time frame used in this study.

FFQ was administrated at the baseline (FFQ1) and one year later (FFQ2) at rural health clinics by trained interviewers with a face-to face approach. Six times 3-day 24-hour recalls (24HRs) surveys were performed between the two FFQs in every two month. The first 24HRs were performed one month later after the FFQ1. Several interviewers visited to participants with local dialect. All participants were asked to recall all foods (including recipes/ingredients of mixed dishes) and drinks that they consumed from the last day (22:00) to next day (22:00) on the 24-hour dietary recall questionnaires in three consecutive days (including two weekdays and one weekend day). The reliability of FFQ was assessed by comparing the dietary pattern scores between FFQ1 and FFQ2. The Validity of the FFQ was assessed by comparing the dietary pattern scores between FFQs and 24HRs.

Fig 2. Bland–Altman plots for scores of prudent pattern and processed food pattern derived from FFQ1and FFQ2.

A: Prudent pattern; B, Processed food pattern; FFQ1-FFQ2, the patterns score difference of FFQ1 and FFQ2; (FFQ1+FFQ2)/2, average pattern scores of FFQ1 and FFQ2. The solid line represents the mean difference (FFQ1-FFQ2) and the dash lines represent the limits of agreements (mean difference ± 1.96 standard deviations).

Fig 3. Bland–Altman plots for scores of prudent pattern and processed food pattern derived from two FFQs and 24HRs.

A, Prudent pattern (FFQ1 vs. 24HRs); B, Processed food pattern (FFQ1 vs. 24HRs); C, Prudent pattern (FFQ2 vs. 24HRs); D, Processed food pattern (FFQ2 vs. 24HRs); FFQs- 24HRs, the pattern score difference of FFQs and 24HRs; (FFQs + 24HRs)/2, average pattern scores of FFQs and 24HRs. The solid line represents the mean difference (FFQs-24HRs) and the dash lines represent the limits of agreements (mean difference ± 1.96 standard deviations).