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Anthropometric data can also be collected in nutrition surveys. A random sample of children is selected from the population. These children are then weighed and measured and the prevalence of malnutrition (whatever form you are interested in) is then calculated from the sample of children.
If the sample upon which the survey is based is representative of the larger population, surveys allow estimation of the prevalence rates in the population because survey data contain both the numerator and denominator of the prevalence, that is, both the number of individuals with malnutrition and the total number of individuals assessed for malnutrition. Surveillance data rarely provide the denominator of prevalence rates.
Nonetheless, nutrition surveys have many problems:
- They often provide very little information about the underlying causes of malnutrition (for more information, see pages on Malnutrition - Introduction and background). Such data are difficult to collect during a short interview.
- Surveys are expensive and time-consuming. They also require a level of technical expertise which is often absent in humanitarian emergencies.
- There are many potential sampling mistakes which may prevent the sample from being truly representative of the population. For example
- Selecting random households, and then selecting only one child in each selected household. For a further explanation of this mistake, click here.
- Weighing and measuring only children who are at home at the time of the survey team's visit. Absent children may have been taken to the clinic and therefore may be more ill, and subsequently malnourished, than children at home. Or, alternately, absent children may be well enough to travel with the mother, so they may be in better health and nutritional status.
- Inclusion of many children older than the target group because, instead of accurately measuring age, survey teams use height criteria to determine a child's eligibility. The prevalence of acute protein-energy malnutrition declines with age, so inclusion of older children will underestimate the prevalence in the target group.
These and other issues of sampling are discussed more fully in the following manuals.
Click here for "Measuring Mortality, Nutritional Status, and Food Security in Crisis Situations: Smart Methodology." SMART Initiative 2006.
Click here for "A Manual: Measuring and Interpreting Malnutrition and Mortality." World Food Programme and US Centers for Disease Control and Prevention 2005.