Causes and Mechanisms of Linear Growth Retardation (International Dietary Energy Consultative Group - IDECG, 1993, 216 pages): Guidelines for the study of mechanisms involved in the prevention or reversal of linear growth retardation in developing countries: Sample size

Causes and Mechanisms of Linear Growth Retardation (International Dietary Energy Consultative Group - IDECG, 1993, 216 pages)

Guidelines for the study of mechanisms involved in the prevention or reversal of linear growth retardation in developing countries

		(introductory text...)
		Introduction
		Background
		The design of research on stunting
		Approaches to the study of stunting
		Sample size
		Potential experimental models for clinical trials
		Examples of useful measurements

Sample size

The research should take the form of a controlled trial involving a sufficient number of children to detect a 0.5 to 1.0 SD difference in length, with a significance of 0.05 and a power of 0.8. If two groups are to be compared, this implies the following sample size per group:

*Difference in length SD*	*N per group*
0.5	64
0.6	45
0.7	34
0.8	26
0.9	21
1.0	17

If more than two groups are compared this increases the sample size needed for each group; when more comparisons are made the chance of a Type 1 error is increased.

In order to reduce the influence of confounding factors it is often useful to make the groups as similar as possible in terms of, for example, initial height-for-age, sex, ethnicity, etc. Larger differences in length velocity may be seen more readily at younger ages, when growth is more rapid.

Studies should be conducted in ecological settings that have a high prevalence of stunting or where a useful factor could be isolated as a variable for testing (e.g. altitude, iron deficiency anaemia, etc.).