Algorithms for converting NCHS references
Summary of published research1
One of the challenges thrown up by the development and introduction of the new WHO growth standards is that surveys using the new growth references cannot be compared with earlier surveys using the NCHS derived references. In order to obtain comparable data over time, earlier surveys would need to be reanalysed using the new WHO standards, however, reanalysis is impossible for older surveys since the raw data are not available. A recently published paper provides algorithms for converting estimates of child malnutrition based on the NCHS reference into estimates based on the WHO standards.
Sixty-eight surveys from the WHO Global Database on Child Growth and Malnutrition were analysed 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 of the predicted WHO prevalence were compared to the observed prevalence.
In total, 271 data points were used to develop the algorithms. The correlation coefficients 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% confidence interval of the predicted estimate containing the observed prevalence was above 90% for all four indicators.
The authors conclude that in order to obtain comparable data concerning child malnutrition, individual survey data should be analysed using the WHO standards. When the raw data are not available, the algorithms developed in the study provide a highly accurate tool for converting existing NCHS estimates into WHO estimates.
1Yang. H and de Onis. M (2008). Algorithms for converting estimates of child malnutrition based on the NCHS reference into estimates based on the WHO Child Growth Standards. BMC pediatrics, pp 1- 6. http://www.biomedcentral.com/1471-2431/18/19
More like this
FEX: New WHO growth standards
This New WHO Growth Standards for infants and children up to 60 months of age, highlighted in Field Exchange 27, are now available. The standards were developed using data...
FEX: Letter on WHO 2006 Growth Standards, by Marko Kerac and Andrew Seal
This new 2006 WHO Growth standards: What will they mean for emergency nutrition programmes? Dear Editor Whilst welcoming the principles which have driven the development of...
FEX: Effect of nutrition survey ‘cleaning criteria’ on estimates of malnutrition prevalence and disease burden: secondary data analysis
Summary of research1 Location: Global What we know: Standardised methods for collection and reporting malnutrition prevalence data in nutrition surveys are used. What this...
en-net: Is it valid to use similar cut-off points for prevalence of wasting using z scores for different countries and contexts?
Hi there, II faced this situation and want to to hear your ideas. We have a programme running for long, but the GAM rates during the hunger gap based on WHO standards 2006 is...
FEX: Developing regional weight-for-age growth references to optimise age-based dosing of anti-malarials
Summary of research1 Location: Global What we know: Age is often used as a proxy for weight in anti-malarial drug dosing. Accurate knowledge of the weight-for-age...
FEX: WHO Growth Standards to assess Indonesian children < 2 years
Summary of published research1 A recent study set out to assess the implications of adopting the WHO Child Growth Standards to classify Indonesian children according to...
FEX: Impact of WHO Growth Standards on programme admissions in Niger
Summary of research1 Severely malnourished children managed in the MSF-run Centre de Récupération Nutritionnelle Intensive (CRENI) in Maradi, Niger A recent study by...
en-net: Analysis of survey data
Analysis of survey data in EPI INFO 6 and SMART (both against NCHS reference) seems to give different results. Has anyone else faced with the same problem? What is the reason?...
FEX: WHO growth reference for children and adolescents
Summary of published research1 The need for a widely applicable growth reference for older children and adolescents has increasingly been recognised by countries attempting to...
en-net: SE Asian Growth Standards
Hi, Does anyone have information on growth standards for SE Asia, specifically for Vietnam. The WHO growth standards are great reference points for assessing growth, and I know...
FEX: The practical implications of using z-scores: Concern's experience in Angola
by Beth Matthews, Maureen Billiet (Concern field staff Angola) Annalies Borrell (Concern chief nutritionist Dublin). In children the three most commonly used anthropometric...
FEX: Impact of WHO Growth Standards on SAM response to treatment
Summary of published research1 More younger admissions to therapeutic feeding programmes are one of the implications of moving to the new WHO Growth Standards. A recent study...
FEX: Including infants in nutrition surveys
Experiences of ACF in Kabul city Claudine Prudhon is the head of the nutrition department in ACF HQ. Claudine is interested in improving the nutritional management of the under...
en-net: malnutrition rate
Dear All, Urgently want to know in any nutritional survey what is the difference we can expect in the percentage of SAM children we will find using WFH criteria and with MUAC...
FEX: Improving estimates of numbers of children with severe acute malnutrition using cohort and survey data
Summary of Research Isanaka S, Boundy EO, Graise RF, Myatt M and Briend A. (2016). Improving Estimates of Numbers of Children With Severe Acute Malnutrition Using Cohort and...
en-net: Urgent: Weight for Height Z-scores: Unisex Z-score table used in West African countries vs. calculated Z score values
In the 2011 Guidelines for THE INTEGRATED MANAGEMENT OF SEVERE ACUTE MALNUTRITION published by ACF, Annex 4 depicts a Weight-for-Height table. This same table has been adopted...
FEX: Can anthropometry measure gender discrimination?
Summary of published research1 A baby girl in Bangladesh. Sex differences in life expectancy and child survival in Bangladesh have been attributed to discrimination against...
en-net: Concern Worldwide is looking for a Nutrition Survey Consultant in Aweil, Southern Sudan
Concern Worldwide/South Sudan Programme Terms of Reference for Consultant to carry out nutritional survey in Aweil North and West Counties, Northern Bahr el Ghazal State, South...
FEX: Effect of adding RUSF to ageneral food distribution on child nutritional status and morbidity: a cluster randomised controlled trial
Summary of research1 Child during appetite test at a health facility offering treatment in Monrovia, Liberia The authors of a recent study hypothesized that including a daily...
FEX: Assessment of the PROBIT approach for estimating the prevalence of acute malnutrition from population surveys
Summary of research1 Location: N/A What we know already:Prevalence of GAM is normally estimated using two stage cluster sampled surveys using the SMART method. The PROBIT...
Reference this page
H Yang and M de Onis (2008). Algorithms for converting NCHS references. Field Exchange 34, October 2008. p10. www.ennonline.net/fex/34/converting