Perhaps the best known and widely used indicator of nutrition is weight for age. This indicator was used in the early 1940s by Gomez and others in the identification of the malnourished for treatment: they compared the weight of children on admission to hospital with the weight of a normal child of the same age to assess whether or not a child was deficient in weight. Thereafter, for the purpose of treatment, they graded the level of nutrition of the children into three groups: if the observed weight was between 75 and 89 per cent of the reference values, the child was considered to be suffering from first degree malnutrition; if between 60 and 74 per cent second degree malnutrition, and
if less than 60 per cent third degree malnutrition (Gomez et al., 1956:77). Later many
workers have preferred to use 80 per cent and 60 per cent as cut-off points.
This system of assessment and grading, popularly known as the 'Gomez classification’, has been used in many countries for the identification of malnourished children and has formed the basis for charting growth in nutritional surveillance programmes (WHO, 1963, 1978; Morley and Woodland, 1979; Wray and Aguirre 1969:78). This indicator shows the extent of underweight of a child compared to median weight of a child of that age in the reference population.
Height (or length) for age, measures the linear or the skeletal growth. The height (or length) of a child does not vary quickly in response to short-term health and economic changes. Height can increase but can not decrease. Since changes in length take place comparatively slowly; as a result, short-term changes in the growth pattern cannot be detected from this measure. Hence, theoretically this may not be the best indicator for predicting the risk of subsequent morbidity and mortality, unless severe long-term effects will include severe reductions in both weight and height of a child
(Behar, 1981:242). It is an indicator of past (and also continuing) or long-term problems in food intake and health.
In many populations secular trends in growth have been accompanied by the increases in stature; therefore, this indicator is very important in assessing the secular trends in nutritional levels (Johnston and Lampl, 1984:58). Low height (or length) for age is normally caused by inadequate food intake with or without the added influence of infections (Waterlow, 1978:457). Height for age is also considered as a good indicator of social deprivation and thus its high prevalence signifies the presence of a serious social and economic problem (Waterlow, 1984:86). Compared with weight, accurate measurement of height (length) requires greater measuring skills and experience.
The weight for height (length) indicator, by contrast, measures body size according to attained height (length). The measurement of tissue mass can change quickly according to the most recent food intake and health condition of the child. Consequently, weight for height (length) is a very useful indicator of recent malnutrition. Deficits in weight for height (length) can develop and disappear very
quickly. As such it is a good indicator to assess the very short-term changes in
nutritional status.
However, it is not an efficient indicator to use for assessing long-term changes in nutritional status (Waterlow, 1984:84). Weight for height (length) as a measure of nutritional assessment is free from the errors arising out of deficient age reporting to which the other two measures are often subject To construct this index, values for both weight and height (length) are needed. The main disadvantage of this indicator is that it is often difficult to measure the body length of very young children accurately. As it is a nutritional indicator which expresses weight in relation to height (length), it does not give any information on the duration (or past level) of nutrition (Keller, Donoso and DeMaeyer, 1976:599).
Among the three anthropometric measurements, weight for age has the advantage that it is relatively easy to measure with a minimum degree of training and with reasonable accuracy. Studies conducted elsewhere have found that this measure
can be used as a predictor of under five mortality (Chen, Chowdhury and Huffman, 1980; Kielmann and McCord, 1978). One of the drawbacks of the measure of weight for age is its inability to detect cases with severe malnutrition (specifically, cases of kwashiorkor with oedema). When these conditions are present, the weight of the child increases because of fluid retention can potentially push the weight for age of an undernourished child above the cut-off point of 60 per cent of the median reference weight for age (Keller, 1983:132). Weight for age being a reflection of both linear and soft tissue is a composite indicator of long-term and short-term malnutrition. The former condition — long-term undemutrition — is also known as 'stunting' and short term undemutrition as 'wasting' (Waterlow, 1972). Weight for age values do not permit the distinction between children who are stunted and fat and children who are tall and wasted. In other words, it does not indicate whether the observed low weight for age is due to a recent food (or health) problem or to a long-term undemutrition problem. This distinction is particularly important in the classification and treatment of an individual
child (Seoane and Latham, 1971; Waterlow, 1972). These deficiencies and the
drawbacks of weight for age as a measure of nutrition, were discussed at length by the 1971 joint Food and Agricultural Organization/World Health Organization expert committee on nutrition (WHO, 1971). The Wellcome Trust Group attempted to rectify some of these drawbacks by proposing a classification which permits the identification of nutritional conditions such as marasmus, kwashiorkor, and nutritional dwarfism
(Wellcome Group, 1970:302-303). Such classification was also found to be less
effective and has failed to consider several deficiency conditions (McLaren, 1971) and is useful in hospital and clinical studies than in field surveys.
In the middle of the 1970s alternative anthropometric indicators such as the mid- arm circumference, weight for height and height for-age were introduced and recognized
for nutritional assessments (Waterlow, 1972). In 1976 the joint FAO/UNICEF/WHO
expert committee on nutrition, recommended the inclusion of weight for height and height for age in the nutritional assessment of infant and pre-school children and
1976). After considering the problems associated with the indicator of weight for age, and in accordance with the recommendations by the Joint Expert Committee of 1976,
Waterlow et al. (1977) put forward guidelines for the use and interpretation of the data
relating to weight and height for the assessment of nutritional status of children 1-10 years; for this age group they endorsed the use of both weight for height and height for age as primary indicators of child nutrition. They recognized that weight for age is a
valid index when the height data are highly unreliable (Waterlow et al.y 1977:491).
In most developing countries there are large proportions of children of pre school age who do not have adequate weight for their age, but do not have noticeable impairments in health. The majority of these children can be considered normal when their weight in relation to attained height is considered. They are short because of inadequate growth in the past and are not undernourished at present. If weight for age is used as the indicator of malnutrition then these children will be classified as undernourished, which is far from the actual situation (Behar, 1981:241). In a society where long-term undemutrition is common, weight for age will not be a good indicator of recent undemutrition and overstates the prevalence of undemutrition (Anderson, 1979:2341).
Keller examined the correlation between the values of the three anthropometric indicators discussed above, and showed that among them weight for height and height for age are virtually independent of each other as they measure two completely different aspects of nutrition (Keller, 1983). He then examined the effects of values of weight for height and height for age on weight for age in terms of standard deviation units and found that 95 to 98 per cent of the variation in weight for age was due to variation in weight for height. Keller attributed the remainder of the variation to measurement error (Keller, 1983). On the basis of these observations, Keller and Filmore concluded that
'weight for age duplicates but does not add to the information obtained from more
specific indicators, height for age and weight for height' (Keller and Filmore, 1983:133; emphasis added). They added that using height for age and weight for height in the assessment of malnutrition in field surveys will give a clearer picture of the type of malnutrition and also allow the determination of priorities for intervention.
A World Health Organization Working Group which reviewed 'the purpose, use and the interpretation of anthropometric indicators of nutritional status' also favoured using weight for height as the indicator of current malnutrition. They recognized weight for age as an indicator of nutrition which can be used to obtain an overview of a nutritional situation or its changes in a country, but stated that the indicator of weight for height alone is sufficient for counting the malnourished (WHO, 1986:936).
Despite its limitations, weight for age is still considered a useful indicator for several reasons: this indicator is basically preferred by the program personnel because it is easy and simple to record provided that the weighing scales are good (Hansen, 1984:96); it has also been found that weight for age correlates well with socio-economic indicators (Hansen, 1984), and thus it is considered one of the most useful development
indicators (Dowler et al., 1982); the other reason that this indicator is increasingly being
used is that, since it overstates the actual prevalence, it helps to emphasize the seriousness of the problem so that policy makers will act quickly (Waterlow, 1984:86).
Although the basic data for certain socio-economic groups are shown according to the weight for age indicator, the focus of this research is on length for age, to study long-term undemutrition, and weight for length for the study of more recent under nutrition.