Abstract
Objective
Community health surveys often collect self-report data on body height and weight for the purposes of calculating the Body Mass Index (BMI) and identifying cases of overweight and obesity. The aim of the study was to test the validity of this method and to describe age and gender trends in self-report bias in height, weight, and BMI.
Methods
This population survey included 4,615 adolescents and adults from across Canada who were interviewed and then measured in their homes. Overweight and obesity were identified using self-reports and cut points in BMI.
Results
Self-reports correlated highly with body measurements but on average, self-reported height was 0.88 cm greater than measured height, self-reported weight was 2.33 kg less than measured weight, and BMI derived from self-reports was 1.16 lower than BMI derived from measurements. Consequently, self-reports yielded lower rates of overweight (31.87%) and obesity (15.32%) than measurements (33.67% and 22.92%, respectively). The magnitude and variability of self-report bias in BMI were related to female gender, older age, and the presence of overweight or obesity.
Discussion
Comparison of self-reported and measured height and weight indicated that most survey respondents under-reported weight and over-reported height. Intentional or not, these biases were compounded in the BMI formula and affected the accuracy of self-reports as a tool for identifying weight problems. Self-reports may be easier to collect than body measurements but should not be used exclusively as an obesity surveillance tool.
Key words: Body mass index, obesity, overweight, self-report bias, validity
Résumé
Objectif
Dans les enquêtes sur la santé dans les collectivités, on recueille souvent des données auto-évaluées sur la taille et le poids pour calculer l’indice de masse corporelle (IMC) et repérer les cas de surpoids et d’obésité. Nous avons voulu éprouver la validité de cette méthode et décrire les tendances d’âge et de sexe dans le biais d’auto-évaluation de la taille, du poids et de l’IMC.
Méthode
Enquête démographique auprès de 4 615 adolescents et adultes au Canada, interviewés puis mesurés à domicile. Le surpoids et l’obésité ont été repérés selon l’auto-évaluation des intéressés et les points limites de l’IMC.
Résultats
Les auto-évaluations affichaient une forte corrélation avec les mensurations, mais en moyenne, la taille déclarée par l’intéressé faisait 0,88 cm de plus que la taille mesurée, le poids déclaré par l’intéressé faisait 2,33 kg de moins que le poids mesuré, et l’IMC dérivée des autoévaluations était inférieur de 1,16 à l’IMC dérivé des mensurations réelles. Par conséquent, les autoévaluations ont donné des taux de surpoids et d’obésité inférieurs aux taux mesurés (31,87 % c. 33,67 % pour le surpoids, et 15,32 % c. 22,92 % pour l’obésité, respectivement). L’ampleur et la variabilité du biais d’auto-évaluation dans le calcul de l’IMC étaient liées au sexe féminin, à la vieillesse et à la présence de surpoids ou d’obésité.
Discussion
La comparaison de la taille et du poids déclarés par l’intéressé et mesurés montre que la plupart des répondants de l’enquête disent avoir un poids inférieur et une taille supérieure à leurs mensurations réelles. Qu’ils soient voulus ou non, ces biais sont aggravés lors du calcul de l’IMC et font en sorte que les auto-évaluations manquent de précision en tant qu’outils de repérage des problèmes de poids. Les auto-évaluations sont plus faciles à obtenir que la prise de mensurations, mais elles ne doivent pas être la seule mesure utilisée pour la surveillance de l’obésité.
Mots clés: indice de masse corporelle, obésité, surpoids, biais d’auto-évaluation, validité
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