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Estimates are based on data from the second cycle (2009 to 2011) of the Canadian Health Measures Survey (CHMS). The CHMS is an ongoing survey designed to provide comprehensive direct health measures data at the national level.15 Ethics approval was obtained from Health Canada's Research Ethics Board.16 The 2009 to 2011 CHMS covered the population aged 3 to 79 in private households. It excluded residents of Indian Reserves, institutions and some remote regions, and full-time members of the regular Canadian Forces. More than 96% of the population aged 3 to 79 is represented.17

Data were collected at 18 sites across Canada from August 2009 to December 2011. In addition to a questionnaire administered in the respondent's home, the survey involved physical measures (including height and weight) in a mobile examination centre. Participation was voluntary. Written informed consent was obtained from respondents aged 14 or older. For younger children, a parent or legal guardian provided written consent, in addition to written assent from the child (where possible). The CHMS Cycle 2 Data User Guide17 contains details about the 2009 to 2011 survey content and sample design.

Of the households selected for the survey, 75.9% agreed to participate. In each responding household, one or two members were selected: 90.5% of selected household members completed the household questionnaire, and 81.7% of the responding household members participated in the subsequent physical measures component. The final response rate, after adjusting for the sampling strategy, was 55.5%.17 This article is based on 2,123 respondents aged 5 to 17, for whom measured values of height and weight were collected.

Height was measured to the nearest 0.1 centimetre using a ProScale M150 digital stadiometer (Accurate Technology Inc., Fletcher, USA), and weight, to the nearest 0.1 kilogram with a Mettler Toledo VLC with Panther Plus terminal scale (Mettler Toledo Canada, Mississauga, Canada).

Body mass index was derived as weight in kilograms divided by height in metres squared. Based on BMI, children and adolescents were classified according to thinness, normal weight, overweight or obesity using two sets of age- and sex-specific cut-offs, one set specified by the WHO,18 and the other, by the IOTF.13,14

The WHO cut-off criteria used to classify children younger than age 5 as overweight or obese19 differ slightly from those used for children aged 5 or older,18 and the WHO does not recommend combining across age groups. Because the sample size for 3- and 4-year-old children in the 2009 to 2011 CHMS was too small to provide reliable estimates using these cut-offs, this age group was not included in this report.

All estimates were based on weighted data. Statistical analyses were performed using SAS and SUDAAN software. Standard errors, coefficients of variation and 95% confidence intervals were calculated with the bootstrap technique.20,21 The number of degrees of freedom was specified as 13 to account for the 2009 to 2011 CHMS sample design.17 Significance levels were set at p <0.05.