Reproducibility and relative validity of a food frequency questionnaire developed among reproductive-aged women in Northeast China

Abstract

Background: To evaluate the reproducibility and relative validity of a newly developed 118-item food frequency questionnaire (FFQ) for assessing habitual dietary intake among reproductive-aged women in Northeast China. Methods: A total of 207 eligible reproductive-aged women were enrolled. After exclusions for incomplete records or implausible energy intakes, 192 completed two FFQs (FFQ1 [first FFQ administration] and FFQ2 [second FFQ administration]) 9 months apart, 182 completed the FFQ and four planned 4-day weighed diet records (WDRs). Reproducibility was assessed using crude and energy-adjusted Spearman correlation coefficients (SCC), intraclass correlation coefficients (ICC), weighted kappa (κw), and quartile misclassification. Relative validity was assessed against WDRs using crude, energy-adjusted, and de-attenuated SCC, κw, and quartile misclassification. Results: For reproducibility, energy-adjusted SCC ranged from 0.32-0.60 (median 0.48) for food groups and 0.30-0.58 (median 0.44) for nutrients; κw ranged from 0.24-0.56 (median 0.43) and 0.26-0.53 (median 0.37), respectively. For validity, de-attenuated SCC ranged from 0.32-0.75 (median 0.57) for food groups and 0.29-0.58 (median 0.48) for nutrients. Same-or-adjacent quartile classification ranged from 76.15%-92.25% (median 85.72%) for reproducibility and 66.94%-85.48% (median 78.23%) for validity, with low extreme misclassification (median < 5% for both). Conclusions: The FFQ demonstrated acceptable reproducibility and relative validity for ranking the habitual intake of most foods and nutrients among reproductive-aged women in Northeast China, supporting its use in epidemiological studies of diet and reproductive health.