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Anthropometric data may be collected by nutrition surveillance. The most common form of surveillance is collection of data from routine growth monitoring programmes in maternal-child health or primary care clinics. However, because of the following problems, these data may not be very useful in emergencies:
- Growth monitoring data reflect the nutritional status of only those children who come for growth monitoring. These children may be healthier than average because they have parents who understand the importance of preventive services. Or they may be worse off than normal because their parents are concerned about their health. When examining growth monitoring data, you don't know which is true.
- Growth monitoring programmes usually collect only sex, age, and weight. No height is measured. Therefore, it is impossible to examine weight-for-height or other measures of acute protein-energy malnutrition, which is the most important form of malnutrition in most humanitarian emergencies.
- Growth monitoring measurements are often taken by clinic workers who have many other duties. Such measurements may not be very accurate. Estimating the prevalence of malnutrition in a population requires data with very little systematic bias. This may not be true of growth monitoring data.
- Growth monitoring data provide no information about the causes or context of malnutrition. The only data available are usually anthropometric measurements.
- In many humanitarian emergencies, growth monitoring, as well as most other curative and preventive health services, often break down because of population displacement, absent health workers, and general insecurity. As a result, timely data on malnutrition are not available.
Many people refer to "nutrition surveillance" when they are actually talking about repeated surveys. However, surveillance is generally defined as below:
Systematic ongoing collection, collation, and analysis of data and the timely dissemination of information to those who need to know so that action can be taken.
-- World Health Organization
The ongoing systematic collection, analysis, and interpretation of health data, essential to the planning, implementation, and evaluation of public health practice, closely integrated with the timely dissemination of these data to those who need to know.
-- U.S. Centers for Disease Control and Prevention
As both definitions above state, surveillance is the ongoing collection of data. A series of surveys are more an episodic than ongoing data collection. This may seem a minor semantic issue, but surveys and surveillance data have very different advantages and disadvantages, especially when the data are used to estimate the prevalence of some health or nutrition outcome in the population. If data from surveys are called surveillance, listeners or readers might think that the data:
- May not be population-based
- May be subject to the reporting and selection biases of surveillance
- May not include the denominator of prevalence rates