Reproducibility of self-administered questionnaire in epidemiological surveys

We evaluated the reproducibility of data on intake frequency of 33 food items, beverage intake frequency of 3 items, drinking and smoking habits, and past history of 10 diseases obtained from a self-administered questionnaire. The survey subjects consisted of 263 aged 39 to 79 years individuals in the general population. After about one year interval these subjects consecutively participated in two surveys and were unintentionally requested to answer to the same questionnaire. The means of percent exact agreements for 33 food items were 48.4% in all, 42.7% in males and 49.4% in females. The means of their percent agreements within one category difference were 85.4% in all, 83.3% in males and 85.8% in females. The reproducibility of beverage intake frequency was the highest in green tea, followed in order by black tea and coffee. The percent exact agreements were 85.4% in males and 81.8% in females for drinking habit, 87.5% in males and 99.0% in females for smoking habit, and 93.7% in males and 97.2% in females for past history. The reproducibility of the self-administered questionnaire was the highest in past history, followed in order by smoking habit, drinking habit and dietary habit. The values of reproducibility were higher in females than in males except for drinking habit. Although reduction of categories was needed to improve the reproducibility, the obtained values from the self-administered questionnaire were sufficiently high for epidemiological studies.