Identification of the Appropriate Boundary Size to Use When Measuring the Food Retail Environment Surrounding Schools

This study included 6,971 students in grades 9 and 10 (ages 13 to 16 years) from 158 schools who participated in the 2009/2010 Health Behaviour in School-aged Children Study. Students provided information on where they typically ate lunch. The number of food retailers was obtained for six road network buffer sizes (500, 750, 1,000, 1,500, 2,000, and 5,000 meters) surrounding schools. Associations between the presence of food retailers near schools and students' lunchtime eating behaviours were examined using multilevel logistic regression. Comparisons of model fit statistics indicated that the 1,000 m buffer provided the best fit. At this distance, students with >= 3 food retailers near their schools had a 3.42 times greater relative odds (95% CI: 2.12-5.52) of eating their lunchtime meal at a food retailer compared to students with no nearby food retailers. Students who had >= 2 food retailers within 750 m of their schools had a 2.74 times greater relative odds (95% CI: 1.75-4.29), while those who had >= 1 food retailer within 500 m of their schools had 2.27 times greater relative odds of eating at food retailer (95% CI: 1.46-3.52) compared to those with no nearby food retailers. For distances greater than 1,000 m, no consistent relationships were found.