MONITORING THE GROWTH OF CHILDREN - CONCLUSIONS FROM A LONG-TERM STUDY

Background. The National Study of Health and Growth (NSHG) was set up in 1972 to monitor the growth of primary school children. Areas were selected in England and Scotland by stratified random sampling. Schools within these areas were visited annually until 1982, biennially thereafter, resulting in a mixed longitudinal design. The reasons for the original design and the study as it has operated are reviewed, with advantages and disadvantages compared to the monitoring system now to be implemented by the Department of Health. Methods. Description of the statistical and interpretive problems of monitoring rates of growth and a comparison of the response rates achieved in the two types of monitoring. Results. Although the design of the NSHG was selected in order to monitor rates of growth this presents statistical problems. The usable information is contained in trends in attained height rather than in rates of growth. This study has achieved an average response rate of over 95%; less than 78% can be expected from the proposed survey of households. Conclusions. The small loss of efficiency of the mixed longitudinal design compared with repeated cross-sectional studies is more than compensated for by its high response rate and the comparability of data over time, neither of which can be guaranteed by the proposed survey.