Three estimates of the association between linear growth failure and cognitive ability.
OBJECTIVE
To compare three estimators of association between growth stunting as measured by height-for-age Z-score and cognitive ability in children, and to examine the extent statistical adjustment for covariates is useful for removing confounding due to socio-economic status.


METHODS
Three estimators, namely random-effects, within- and between-cluster estimators, for panel data were used to estimate the association in a survey of 1105 pairs of siblings who were assessed for anthropometry and cognition. Furthermore, a 'combined' model was formulated to simultaneously provide the within- and between-cluster estimates.


RESULTS
Random-effects and between-cluster estimators showed strong association between linear growth and cognitive ability, even after adjustment for a range of socio-economic variables. In contrast, the within-cluster estimator showed a much more modest association: For every increase of one Z-score in linear growth, cognitive ability increased by about 0.08 standard deviation (P < 0.001). The combined model verified that the between-cluster estimate was significantly larger than the within-cluster estimate (P = 0.004).


CONCLUSIONS
Residual confounding by socio-economic situations may explain a substantial proportion of the observed association between linear growth and cognition in studies that attempt to control the confounding by means of multivariable regression analysis. The within-cluster estimator provides more convincing and modest results about the strength of association.
Cheung
Y B
YB
Biostatistics Unit, Singapore Clinical Research Institute, Singapore. yinbun.cheung@scri.edu.sg
Lam
K F
KF
D002648:Child; D002657:Child Development / Q000502:physiology*; D003071:Cognition / Q000502:physiology*; D004812:Epidemiologic Methods; D005260:Female; D006130:Growth Disorders / Q000453:epidemiology / Q000523:psychology*; D006801:Humans; D008297:Male; D010679:Philippines; D011594:Psychometrics; D012959:Socioeconomic Factors