The paper by Seal and Kerac has prompted queries from concerned users
of the software World Health Organization (WHO) Anthro 2005. The paper
states that "the available software for the WHO growth standards (WHO
Anthro 2005) fail to distinguish between children with wasting and those
with oedema" (page 2) and that "the program fails to separate cases with
oedema and account for them as a separate category of severe malnutrition
in its summary statistics....this may have the effect of falsely reducing
the reported prevalence of nutritional oedema" (page 5). Both these
statements are incorrect. The software WHO Anthro 2005 does include cases
with oedema in the prevalence of cases classified as wasted (<-2
standard deviation (SD) weight-for-height) and severely wasted (<-3 SD
weight-for-height), making it consistent with standard reporting systems.
In addition, it reports the number of cases in the data set that had
oedema.
Further the paper presents an analysis of the WHO Child Growth
Standards that is incorrect both from a conceptual and an epidemiological
point of view. The authors have manipulated the WHO standards to recreate
weight-for-height reference values in a way that does not respect the
methodology used to construct the original standards. The use of the
percent-of-median classification is inappropriate because it ignores the
inherent skewness of weight-based indicators. Therefore, the newly created
values cannot any longer be referred to as the "WHO standards". With the
newly created values (misleadingly still referred to as the "WHO
standards") the authors proceed to do an inappropriate comparison of the
original WHO z-score values (to derive prevalences of severe malnutrition)
with their newly derived "WHO values" in percent-of-median (to screen
individual children for selective feeding programmes). The authors
conclude that the two applications of the standards do not yield
consistent results and describe this as paradoxical. Indeed, different
results are to be expected as two different sets of values (i.e. the
original WHO values and the values derived by the authors) and two
different classification systems (ie, z-scores and percent-of-median) are
used in the comparison.
The paper has other inaccurate statements. For example, it equates -
2SD with 80% of median and -3SD with 70% of median. These cut-offs
classify children differently and those working in nutrition programmes
are familiar with the problems this entails. Furthermore, the authors
state that percent-of-median is a widely used tool in nutrition
programmes. As shown by a global survey on growth monitoring practices (1)
only 6% of national programmes use the percent-of-median classification
system compared with 63% using percentiles and 18% using z-scores. As a
matter of fact none of the existing growth references have presented
percent-of-median reference values.
In sum, it is regrettable that the paper will likely add more
confusion than clarity to a field that is in need of clear concepts.
1. de Onis M, Wijnhoven TMA, Onyango AW. Worldwide practices in child
growth monitoring. J Pediatr 2004;144:461-5.
Competing interests:
We coordinate the WHO Child Growth Standards project.
Rapid Response:
On the WHO Child Growth Standards
The paper by Seal and Kerac has prompted queries from concerned users
of the software World Health Organization (WHO) Anthro 2005. The paper
states that "the available software for the WHO growth standards (WHO
Anthro 2005) fail to distinguish between children with wasting and those
with oedema" (page 2) and that "the program fails to separate cases with
oedema and account for them as a separate category of severe malnutrition
in its summary statistics....this may have the effect of falsely reducing
the reported prevalence of nutritional oedema" (page 5). Both these
statements are incorrect. The software WHO Anthro 2005 does include cases
with oedema in the prevalence of cases classified as wasted (<-2
standard deviation (SD) weight-for-height) and severely wasted (<-3 SD
weight-for-height), making it consistent with standard reporting systems.
In addition, it reports the number of cases in the data set that had
oedema.
Further the paper presents an analysis of the WHO Child Growth
Standards that is incorrect both from a conceptual and an epidemiological
point of view. The authors have manipulated the WHO standards to recreate
weight-for-height reference values in a way that does not respect the
methodology used to construct the original standards. The use of the
percent-of-median classification is inappropriate because it ignores the
inherent skewness of weight-based indicators. Therefore, the newly created
values cannot any longer be referred to as the "WHO standards". With the
newly created values (misleadingly still referred to as the "WHO
standards") the authors proceed to do an inappropriate comparison of the
original WHO z-score values (to derive prevalences of severe malnutrition)
with their newly derived "WHO values" in percent-of-median (to screen
individual children for selective feeding programmes). The authors
conclude that the two applications of the standards do not yield
consistent results and describe this as paradoxical. Indeed, different
results are to be expected as two different sets of values (i.e. the
original WHO values and the values derived by the authors) and two
different classification systems (ie, z-scores and percent-of-median) are
used in the comparison.
The paper has other inaccurate statements. For example, it equates -
2SD with 80% of median and -3SD with 70% of median. These cut-offs
classify children differently and those working in nutrition programmes
are familiar with the problems this entails. Furthermore, the authors
state that percent-of-median is a widely used tool in nutrition
programmes. As shown by a global survey on growth monitoring practices (1)
only 6% of national programmes use the percent-of-median classification
system compared with 63% using percentiles and 18% using z-scores. As a
matter of fact none of the existing growth references have presented
percent-of-median reference values.
In sum, it is regrettable that the paper will likely add more
confusion than clarity to a field that is in need of clear concepts.
1. de Onis M, Wijnhoven TMA, Onyango AW. Worldwide practices in child
growth monitoring. J Pediatr 2004;144:461-5.
Competing interests:
We coordinate the WHO Child Growth Standards project.
Competing interests: No competing interests