title: Algorithms for converting estimates of child malnutrition based on the NCHS reference into estimates based on the WHO Child Growth Standards.
abstract: BACKGROUND
  The child growth standards released by the World Health Organization (WHO) in 2006 have several technical advantages over the previous 1977 National Center for Health Statistics (NCHS)/WHO reference and are recommended for international comparisons and secular trend analysis of child malnutrition. To obtain comparable data over time, earlier surveys should be reanalyzed using the WHO standards; however, reanalysis is impossible for older surveys since the raw data are not available. This paper provides algorithms for converting estimates of child malnutrition based on the NCHS reference into estimates based on the WHO standards.
  
  
  METHODS
  Sixty-eight surveys from the WHO Global Database on Child Growth and Malnutrition were analyzed using the WHO standards to derive estimates of underweight, stunting, wasting and overweight. The prevalences based on the NCHS reference were taken directly from the database. National/regional estimates with a minimum sample size of 400 children were used to develop the algorithms. For each indicator, a simple linear regression model was fitted, using the logit of WHO and NCHS estimates as, respectively, dependent and independent variables. The resulting algorithms were validated using a different set of surveys, on the basis of which the point estimate and 95% confidence interval (CI) of the predicted WHO prevalence were compared to the observed prevalence.
  
  
  RESULTS
  In total, 271 data points were used to develop the algorithms. The correlation coefficients (R2) were all greater than 0.90, indicating that most of the variability of the dependent variable is explained by the fitted model. The average difference between the predicted WHO estimate and the observed value was <0.5% for stunting, wasting and overweight. For underweight, the mean difference was 0.8%. The proportion of the 95% CI of the predicted estimate containing the observed prevalence was above 90% for all four indicators. The algorithms performed equally well for surveys without the entire age coverage 0 to 60 months.
  
  
  CONCLUSIONS
  To obtain comparable data concerning child malnutrition, individual survey data should be analyzed using the WHO standards. When the raw data are not available, the algorithms presented here provide a highly accurate tool for converting existing NCHS estimates into WHO estimates.
authors.affiliation: Department of Nutrition, World Health Organization, Geneva, Switzerland. yangh@who.int
authors.forename: Hong
authors.initials: H
authors.lastname: Yang
authors.forename: Mercedes
authors.initials: M
authors.lastname: de Onis
mesh_terms: D000465:Algorithms; D015362:Child Nutrition Disorders / Q000175:diagnosis / Q000453:epidemiology*; D002675:Child, Preschool; D006128:Growth; D006130:Growth Disorders / Q000453:epidemiology; D006801:Humans; D007223:Infant; D007228:Infant Nutrition Disorders / Q000175:diagnosis / Q000453:epidemiology*; D007231:Infant, Newborn; D016014:Linear Models; D009309:National Center for Health Statistics, U.S.; D009749:Nutrition Surveys; D009752:Nutritional Status; D050177:Overweight / Q000453:epidemiology; D015995:Prevalence; D012016:Reference Values; D015203:Reproducibility of Results; D013851:Thinness / Q000453:epidemiology; D014481:United States; D019282:Wasting Syndrome / Q000453:epidemiology; D014944:World Health Organization