To maximize data collection during a fixed (regularly scheduled) classroom period while minimizing the number of items per questionnaire, the OSDUHS uses two forms, which are distributed alternately in classrooms.
Further details regarding OSDUHS methodology can be accessed at http://www.camh.ca/research/osduhs.aspx.
Our analyses employed design-based methods to account for the complex survey data of the OSDUHS. This estimation differs from non-survey analysis in two respects.
On the basis of the 2013 OSDUHS data, 25.1% (95% confidence interval: 23.5-26.7) of students in grades 7 through 12 were classified as overweight or obese (Figure 1).
In any case, our use of the 2013 OSDUHS serves as an appropriate baseline for ongoing monitoring of this age group.
(21) Several relevant variables (e.g., body image, weight control, use of diet pills, fruit and vegetable consumption, physical activity and sedentary behaviour) are available in the OSDUHS data.
According to the most recent OSDUHS report, (15 p 49) "experimental work on the OSDUHS showed that the pre-coded format reduced missing value responses versus open-ended formats".