摘要
The mean height-for-age Z-score(HAZ)of children under five is an important indicator of the health status of a population.HAZ values are frequently aggregated and reported at the national level,potentially obscuring important within-country variation.We evaluated aggregation and interpolation methods to provide sub-national estimates over space and time,using survey data from Nigeria in 1990,2003,2008,and 2013.We aggregated HAZ values by region and by state,and interpolated the values spatially and spatio-temporally using thin plate splines.The results were evaluated with cross-validation using the root mean squared error(RMSE)as a measure of goodness of fit.Mean HAZ values increased from 1990 to 2013,but values rose more sharply in southern Nigeria than in the North.All methods performed better than assuming a constant national average.The state-level aggregation,and the spatial and spatio-temporal interpolations had similar RMSE values,but the interpolation methods showed more detailed spatial variation.Spatio-temporal interpolation produced good results in all conditions,including in years with sparse sampling and when extrapolating to years for which there were no observations.
