Validity and reproducibility of a quantitative food frequency questionnaire for a cohort study in Japan

Background: A self-administered quantitative food frequency questionnaire ( Qx) was developed for a population-based cohort study on cancer in Takayama , Japan. Methods: The Qx was tested among 58 male and 59 female volunteers. Average daily nutrient intakes for the previous year calculated from the Qx were co mpared with those from 3-day food records and four 24-h recalls. The Qx was also validated among 37 volunteers by comparing the nutrient intakes calcu lated from the Qx with 12 1-day food records during a year. We also calcula ted the intra-class correlation coefficients for various nutrients between the Qx and the second Qx administered by the same volunteers 1 year after t he first survey. Results: Pearson correlation coefficients between total energy from the Qx and 3-day records were 0.38 for men and 0.25 for women and those between th e Qx and 24-h recalls were 0.19 and -0.02 for men and women, respectively. Correlations between the several nutrients from the Qx and 3-day records ra nged from 0.2 to 0.5 for both men and women. These correlations after energ y adjustment ranged from 0.2 to 0.6 for men and from 0.1 to 0.7 for women. in general, the correlations for various nutrients between the Qx and 12 1- day records were higher than those described above. The intra-class correla tion coefficients ranged from 0.46 to 0.78 in men and from 0.36 to 0.67, ex cept for vitamin C in women. When the information on portion size was exclu ded, almost all of the above indices showed somewhat lower figures. Conclusion: These results suggest that our food frequency questionnaire wit h portion size information can be used to estimate nutrient intakes of each individual.