EASY – An Instrument for Surveillance of Physical Activity in Youth

There is a need for a self-report instrument, with sound psychometric properties, for monitoring compliance with physical activity guidelines in youth. This study aimed to develop such an instrument by applying Item Response Theory as well as traditional methods for assessing validity and reliability. Focus groups, conducted with 162 middle school students, identified 30 forms of physical activity that are highly prevalent in that age group. These activities were incorporated into three preliminary forms of a self-report instrument. The three formats were: yes/no for participation in each activity during the previous seven days; yes/no plus the number of days (1-7) on which the activity was performed; and yes/no, frequency (1-7) and intensity (1-4). Middle school students (n=537) were randomly assigned to complete one of the three instruments. Rasch analysis was applied to the responses to the three formats, and the yes/no plus frequency format was identified as the preferred format. This instrument was completed twice by an independent sample of 342 middle school students at the end of a seven day period during which they had worn an accelerometer. Associations between responses to the individual items and objectively measured moderate to vigorous physical activity (MVPA) resulted in selection of six items for inclusion in the final instrument. Six more items were included on the premise that they should be queried in a surveillance system. Three additional items were included on the basis of a Rasch analysis. This produced a fourteeen item instrument, and responses to this instrument were found to be highly reliable (r=0.91) and demonstrated acceptable concurrent validity when associated with objectively measured MVPA (r=0.33).