Learning from Non-Reported Data: Interpreting Missing Body Mass Index Values in Young Children

The objective of this study was to examine the pattern of relations between missing weight and height (BMI) data and a range of demographic, physical activity, sedentary behavior, and academic measures in a young sample of elementary school children. A secondary analysis of a large cross-sectional study, PLAY-On, was conducted using self-reported data from a convenience sample of fifth-to eighth-grade students (9-14 years) attending 30 elementary schools in Ontario, Canada. Items assessed related to demographics (age, gender, and ethnicity), physical activity (energy expenditure, location, and sport participation), sedentary behavior (communication and screen-time), and academics. Of the 2,111 children who were included in the analyses, 960 (45.5%) were missing BMI data. Children without BMI data were more likely to be younger, female, of non-white ethnicity, have lower daily energy expenditure values, not participate in school sports, and have lower-rated academic standing than those children with BMI data. Overall, this study demonstrates characteristics of children who fail to self-report their height or weight. The trend for younger children to be more likely to fail to report BMI suggests that some children may be unmotivated non-responders. Meanwhile, the trend for girls to be more likely to fail to report weight than boys indicates that some girls may be motivated non-responders. Self-report BMI might include too much missing data to be effective for determining children's progress toward previously established targets for intervention and surveillance efforts.