Yang Hong, de Onis Mercedes
Department of Nutrition, World Health Organization, Geneva, Switzerland.
BMC Pediatr. 2008 May 5;8:19. doi: 10.1186/1471-2431-8-19.
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.
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.
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.
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.
世界卫生组织（WHO）2006年发布的儿童生长标准相较于之前1977年美国国家卫生统计中心（NCHS）/WHO的参考标准具有多项技术优势，被推荐用于儿童营养不良的国际比较和长期趋势分析。为了获得不同时期可比的数据，早期调查应使用WHO标准重新分析；然而，由于无法获取原始数据，对于较早的调查无法进行重新分析。本文提供了将基于NCHS参考标准的儿童营养不良估计值转换为基于WHO标准估计值的算法。
利用WHO全球儿童生长与营养不良数据库中的68项调查，采用WHO标准得出体重不足、发育迟缓、消瘦和超重的估计值。基于NCHS参考标准的患病率直接取自该数据库。使用最小样本量为400名儿童的国家/地区估计值来开发算法。对于每个指标，拟合一个简单线性回归模型，分别将WHO和NCHS估计值的对数几率作为因变量和自变量。使用另一组调查对所得算法进行验证，在此基础上，将预测的WHO患病率的点估计值和95%置信区间（CI）与观察到的患病率进行比较。
总共使用了271个数据点来开发算法。相关系数（R2）均大于0.90，表明拟合模型解释了因变量的大部分变异性。对于发育迟缓、消瘦和超重，预测的WHO估计值与观察值之间的平均差异<0.5%。对于体重不足，平均差异为0.8%。所有四个指标的预测估计值的95%CI包含观察到的患病率的比例均高于90%。对于未涵盖0至60个月整个年龄范围的调查，该算法表现同样良好。
为了获得有关儿童营养不良的可比数据，应使用WHO标准对单个调查数据进行分析。当无法获取原始数据时，本文提出的算法提供了一种将现有NCHS估计值转换为WHO估计值的高精度工具。
