Table 2.
Summary of best practices for growth indicator selection in biomarker association studies
| Studies | Recommended best practices1 |
|---|---|
| Descriptive analysis | |
| All | a. Perform descriptive analysis of HAZ as mean ± SD and median (interquartile range) using WHO child growth standards. b. Express proportion stunted (i.e., HAZ <−2); consider analysis using more categories if sample size and HAZ spread allows. |
| Analyses to look for biomarker association with growth2 | |
| All | a. Linear regression with HAZ: i. A continuous approach can be used for initial analysis. ii. Categorical approaches are advised for more definitive analysis preferably with more than 2 categories, if sample size and HAZ spread allows. iii. More advanced techniques for analyzing nonlinear relations (e.g., quantile regression, regression trees or generalized additive models) are preferred. b. If birth length (or weight) is known, conditional length can be used as an indicator of postnatal growth. |
| Additionally consider when 2 height measurements at least 2 months apart are available3 | a. Change in z-scores of attained height (ΔHAZ), over a time interval of at least 2 months, adjusted for HAZ at either time 1 (forward analysis) or time 2 (backward analysis). b. Conditional height velocity. |
| Additionally consider in studies with >2 height measurements at least 2 months apart3 | a. Change in z-scores of attained height, over a time interval of 3–6 months, adjusted for HAZ at one of the time points. b. Conditional height velocity. c. Random-effects regression models modeling ΔHAZ. |
HAZ, height-for-age z-score; SD, standard deviation.
1
Unadjusted and adjusted models should be run.
2
Principles in this table also apply to weight measurements, although shorter intervals of at least 1-month duration are acceptable when more than one measure is available.
3
If all measurements are among children <24 months of age, in theory the z-score of the increment in length could be a valuable indicator. However, given the lack of availability of validated statistical tools to calculate conditional velocity z-score (adjusted for baseline status), this approach should be considered experimental at this time.