Reproducibility of dietary and other data from a self-administered questionnaire

This study examined the reproducibility of information obtained from a questionnaire covering dietary and other information by comparing the answers to the questionnaires with answers to the same questions one year later. Answers from 191 men and 220 women, aged 40 to 65, in Fukuoka prefecture, Japan were compared. The surveys were conducted in November 1989 and November 1990. In the second survey, 97.2% of the first respondents answered. The concordance between the two responses was high, and the differences between the mean intakes from the two surveys were within 5% for 7 food items and within 15% for 14 food items among the 20 items about which the respondents were asked. The intraclass correlation coefficients varied from 0.30 for eggs to 0.62 for milk, with 16 items greater than 0.4. The differences in reproducibility between the sexes and two age categories were not significant. Close values also were obtained for the estimated consumption of salt. A substantially high reproducibility was observed on items regarding drinking and smoking; most of the kappa statistics and the intraclass correlation coefficients were between 0.5 and 0.9. The above reproducibility on individual food items was comparable to or better than those reported from other studies. The results of the present study thus indicate that the self-administered semiquantitative food intake questionnaire used for our cross-sectional study is useful for epidemiologic studies to assess the association between diet and various diseases. In particular, the present questionnaire is highly dependable regarding the overall group intake of foods. The information on smoking, drinking, and other items obtained by this questionnaire also seemed to be sufficiently reliable for epidemiologic surveys.