Measuring the bias, precision, accuracy, and validity of self-reported height and weight in assessing overweight and obesity status among adolescents using a surveillance system.

BACKGROUND Evidence regarding bias, precision, and accuracy in adolescent self-reported height and weight across demographic subpopulations is lacking. The bias, precision, and accuracy of adolescent self-reported height and weight across subpopulations were examined using a large, diverse and representative sample of adolescents. A second objective was to develop correction equations for self-reported height and weight to provide more accurate estimates of body mass index (BMI) and weight status. METHODS A total of 24,221 students from 8th and 11th grade in Texas participated in the School Physical Activity and Nutrition (SPAN) surveillance system in years 2000-2002 and 2004-2005. To assess bias, the differences between the self-reported and objective measures, for height and weight were estimated. To assess precision and accuracy, the Lin's concordance correlation coefficient was used. BMI was estimated for self-reported and objective measures. The prevalence of students' weight status was estimated using self-reported and objective measures; absolute (bias) and relative error (relative bias) were assessed subsequently. Correction equations for sex and race/ethnicity subpopulations were developed to estimate objective measures of height, weight and BMI from self-reported measures using weighted linear regression. Sensitivity, specificity and positive predictive values of weight status classification using self-reported measures and correction equations are assessed by sex and grade. RESULTS Students in 8th- and 11th-grade overestimated their height from 0.68cm (White girls) to 2.02 cm (African-American boys), and underestimated their weight from 0.4 kg (Hispanic girls) to 0.98 kg (African-American girls). The differences in self-reported versus objectively-measured height and weight resulted in underestimation of BMI ranging from -0.23 kg/m2 (White boys) to -0.7 kg/m2 (African-American girls). The sensitivity of self-reported measures to classify weight status as obese was 70.8% and 81.9% for 8th- and 11th-graders, respectively. These estimates increased when using the correction equations to 77.4% and 84.4% for 8th- and 11th-graders, respectively. CONCLUSIONS When direct measurement is not practical, self-reported measurements provide a reliable proxy measure across grade, sex and race/ethnicity subpopulations of adolescents. Correction equations increase the sensitivity of self-report measures to identify prevalence of overall overweight/obesity status.