title: 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.
abstract: 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.
authors.forename: Adriana
authors.initials: A
authors.lastname: Pérez
authors.forename: Kelley
authors.initials: K
authors.lastname: Gabriel
authors.forename: Eileen K
authors.initials: EK
authors.lastname: Nehme
authors.forename: Dorothy J
authors.initials: DJ
authors.lastname: Mandell
authors.forename: Deanna M
authors.initials: DM
authors.lastname: Hoelscher
mesh_terms: D000293:Adolescent; D015982:Bias; D001827:Body Height; D001828:Body Image; D015992:Body Mass Index; D001835:Body Weight; D005006:Ethnicity; D005260:Female; D006801:Humans; D008297:Male; D050177:Overweight; D063766:Pediatric Obesity / Q000175:diagnosis* / Q000453:epidemiology; D011159:Population Surveillance / Q000379:methods*; D015995:Prevalence; D044469:Racial Groups; D015203:Reproducibility of Results; D057566:Self Report / Q000592:standards*; D012680:Sensitivity and Specificity; D013781:Texas / Q000453:epidemiology