Objectives: The mean number of steps measured in the National Health and Nutrition Survey is employed for the assessment of physical activity/exercise in "Health Japan 21," and is used to represent the amount of physical activity/exercise that citizens engage in. In this study, we clarified the characteristics of the data on the number of steps, drawn from the National Health and Nutrition Survey.
Methods: Among the data from the National Health and Nutrition Surveys conducted from 2008 to 2010, data from 21,914 participants on daily number of steps and pedometer attachment were analyzed. On a nutritional intake questionnaire, subjects who responded on the physical status item that they had attached the pedometer all day long were assigned to the "Whole-day-attached" group. Their means, medians, outliers, and frequency distribution were then compared with those in a "Non- whole-day-attached" group.
Results: Subjects assigned to the "Non- whole-day-attached" group accounted for about 8% of cases in 2008, 2009, and 2010. In all three years, the mean number of steps in the "Whole-day-attached" group was 1,076 to 1,472 higher than that in the "Non-whole-day-attached" group. In both groups, outliers were present, and the frequency distribution showed a broad range on the side indicating a higher number of steps. Accordingly, the mean value was higher than the median value by approximately 600 steps.
Conclusion: As data on the number of steps measured in the National Health and Nutrition Survey includes individuals not attaching the pedometer all day (approximately 8% of cases), the data are not normally distributed. Therefore, when utilizing these data as representative of citizens' physical activity/exercise, their characteristics should be taken into consideration.