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Age standardization of weight-for-height in children using a unified Z-score method
1Shiraz University of Medical Sciences, Islamic Republic of Iran.
Insights
Standard weight-for-height assessments in children are flawed as they ignore age. This study introduces an age- and sex-specific Z-score method for accurate child growth assessment.
Area of Science:
- Pediatric endocrinology
- Human growth and development
- Biostatistics
Background:
- Traditional weight-for-height standards often assume age independence, which is inaccurate for children.
- Existing methods, like Cole's 1979 approach, can lead to assessment errors, particularly for specific age-sex groups.
Purpose of the Study:
- To address the age-dependency issue in assessing children's weight-for-height.
- To propose and validate an alternative method using age- and sex-specific Z-scores for growth assessment.
Main Methods:
- Utilized data from a Shiraz (Iran) growth study of 1207 schoolchildren (aged 6-12).
- Developed a novel method based on Z-scores of height-for-age (HI) and log (weight)-for-age (WI).
- Modeled age- and sex-specific smoothed centile curves for height-for-age and weight-for-age.
Main Results:
- The proposed Z-score method (HI and WI) effectively accounts for age and sex in growth assessment.
- This approach overcomes the limitations of age-independent weight-height relationships.
- Generated age-adjusted weight-for-height centiles for the study population.
Conclusions:
- The Z-score method for assessing child growth is simple, stable, and overcomes age-dependency issues.
- This method is recommended for accurate weight-for-height assessments in children.
- The approach shows potential utility for diverse growth datasets.
Abstract:
Weight-for-height standards in children are usually constructed on the basis that the expected weight for a given height does not depend on age, an assumption which is unjustified. Analysis of data from a Shiraz (Iran) growth study confirms the need to take age into account when assessing weight-for-height of schoolchildren aged 6-12. The method described by Cole in 1979 (Annals of Human Biology, 6, 249-268) leads to errors in the assessment of these children, in particular 6-year-old boys and 10-year-old girls. This paper proposes an alternative, which relies on Z-score of height-for-age (HI) and Z-score of log (weight)-for-age (WI). These indices are age- and sex-specific standard scores (Z-scores) derived from modelling height-for-age and weight-for-age smoothed centile curves. The method provides a unified structure of the regression of WI on HI, which overcomes the problem of age dependency in weight-height relationship. Age-adjusted smoothed centiles of weight-for-height are derived at each age of weight and height to their respective Z-scores, and weight-for-height centiles of 1207 Shiraz schoolchildren in a representative sample in a cross-sectional study are drawn for each age-sex category. This Z-score method proves to be simple and stable, and is likely to be useful for any sort of growth data.