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The relationship between anthropometric indices derived from the CDC/WHO international reference
1Unit for Statistics and Epidemiology, Liverpool School of Tropical Medicine, UK.
Insights
The CDC/WHO weight-for-height Z-score (WHZ) index shows discrepancies in children with low growth percentiles, questioning its use for malnutrition assessment in developing countries.
Area of Science:
- Pediatric Nutrition
- Anthropometry
- Public Health
Background:
- Standard anthropometric indices like weight-for-age (WAZ), height-for-age (HAZ), and weight-for-height (WHZ) are crucial for assessing child growth.
- The CDC/WHO reference is widely used but its suitability across different populations and age groups requires scrutiny.
Purpose of the Study:
- To examine the relationship between WAZ, HAZ, and WHZ scores using the CDC/WHO reference.
- To explore the age-related pattern of WHZ and analyze WAZ/WHZ regressions using Ghana Demographic and Health Survey data.
- To evaluate the validity of the WHZ index for identifying malnutrition in young children in developing countries.
Main Methods:
- Analysis of standard deviation scores for WAZ, HAZ, and WHZ based on the CDC/WHO reference.
- Exploration of WHZ patterns with age for reference children.
- Examination of WAZ on HAZ and WHZ regression using Ghanaian survey data (1988).
Main Results:
- Discrepancies in WHZ indices were observed for reference children with heights and weights at the lower end of the population range.
- A discontinuity in WHZ was noted between 23 and 24 months, reflecting the CDC/WHO reference's data source junction.
- Curvature in WHZ values between 3 and 23 months was apparent, especially for children below the reference median.
Conclusions:
- The CDC/WHO WHZ index exhibits peculiarities that may undermine its accuracy for measuring malnutrition in young children in developing nations.
- Age consistency is essential for a reliable weight-for-height index, a criterion not fully met by the current CDC/WHO WHZ.
- Alternative indices for wasting and updated reference figures are recommended for improved malnutrition assessment.
Abstract:
This paper examines the relationship between the standard deviation scores of weight-for-age (WAZ), height-for-age (HAZ) and weight-for-height (WHZ) calculated using the CDC/WHO reference. The pattern of WHZ with age is explored for CDC/WHO reference children following set paths for WAZ and HAZ, and the nature of the regression of WAZ on HAZ and WHZ is examined for the Ghana Demographic and Health Survey data (1988). Reference children with heights and weights at the lower end of the range for their population showed discrepancies in their WHZ indices. A marked discontinuity between 23 and 24 months reflected the junction between the two data sets from which the CDC/WHO reference was derived. There was also clear curvature in the values for WHZ between 3 and 23 months, particularly apparent for children with weights and heights well below the reference median. While the regression equation for the Ghanaian data was similar to that already described by Keller in 1983, marked curvature was observed in the residual plot for children under 2 years. Consistency with age is a prerequisite for a weight-for-height index. The peculiarities of this index as based on the CDC/WHO reference undermine the validity of its use in measuring malnutrition among young children in developing countries. It is suggested that serious consideration is given to the use of an alternative index of wasting and to the development of alternative reference figures.