Is the national nutrition survey in Japan representative of the entire Japanese population?

Objective We examined the representativeness of the sample used in the National Nutrition Survey in Japan (J-NNS). Methods The distribution of the J-NNS sample from 1995 to 2000 was compared with that of the national census with respect to gender, age group, place of residence, and number of household members. Results In the survey sample, as compared with the national census distributions, the proportion of females was 1% to 2% larger, the proportion of individuals who were 20 to 39 y of age was a few percentages smaller, and a slight bias toward rural areas was seen. Among individuals who were 20 to 59 y of age, the proportion of individuals who lived in single-person households was 50% to 66% of that found in the national census. Observed disparities between the sample and the population were minimal except in the case of the proportion of individuals who lived alone. Conclusions The sample used in the J-NNS is generally representative of the entire Japanese population with the exception of individuals in single-person households.