communicable diseases is collected rou- tinely from health care providers, such as clinic and hospital personnel, both public and private. Nutrition surveillance is also often carried out by reporting anthro- pometry from clinics where growth mon- itoring is done to central public health authorities. Of course, because most sur- veillance data are collected from health facilities, they are relevant to people who come to clinics for curative or preventive care. Often such people are quite differ- ent from those who do not come to health care workers for services. As a result, surveillance data rarely are truly representative of the entire population. As will be described in this chapter, sur- veys can provide just such representative information if carried out correctly. Because surveillance systems gather data continuously over time, such data are especially well suited for following trends in the incidence or prevalence of the dis- ease reported in the system. For example, if the surveillance system has not under- gone major changes in a period of five years, it can show whether the number of cases of a specific disease has increased, decreased or remained the same during this time period. In general, because sur- veys gather data at a single point in time, data from a single survey cannot be used to follow trends. Moreover, because sur- veys collect data on possible contributing factors at the same time they collect data on the disease of interest, you often cannot tell which came first, the risk factor or the disease. For this reason, surveys usually are not the best way to explore causality. To more completely understand nutritional problems in a population, additional infor- mation about the causes of malnutrition should be obtained by other means, such as qualitative assessment techniques.
2. DEFINE SURVEY OBJECTIVES AND DEFINE THE GEOGRAPHIC TARGET AREA TO BE INCLUDED IN THE SURVEY
You must be clear about your objectives before starting a nutrition survey. Precise and clear objectives will make it much easier for your team, collaborating organ- izations, the survey population and donors to understand what you are trying achieve. Clear objectives will also make the analysis of survey data much easier by guiding which analyses will answer the basic questions that prompted the survey. Often, a nutrition survey is undertaken to fulfil the following types of objectives:
• To measure the proportion of individu- als in specific groups, often children 6- 59 months of age or women of child- bearing age, with malnutrition or anaemia. Such data can be used to determine the need for specific nutri- tion interventions.
• To measure the coverage of feeding programs - that is, the proportion of individuals in specific groups who are beneficiaries of a nutrition pro- gram - for example, the proportion of moderately malnourished children who receive food from a supplemen- tary feeding program or the propor- tion of families who have received food from the general ration distribu- tion. These results can measure whether a program is reaching the intended beneficiaries.
• To establish a baseline against which changes in nutritional status over time can be compared by carrying out a fol- low-up survey. Although such data are sometimes used to measure the effec- tiveness of a program, there may be many factors that can influence change over time in addition to the implemen- tation of a specific nutrition program.
Serial surveys meant to demonstrate changes in nutritional status should be planned carefully. For example, baselines and follow-up surveys meant to detect changes over time could be done in the same population and at the same time of year in order to minimize the differences between populations and the effect of sea- sonal changes in nutritional status. In addition, an apparent difference between surveys may be the result only of sampling error, described later in this manual. You should not conclude that a statistically sig- nificant difference exists between the results of two surveys without the use of a statistical test. In addition, surveys over time in an intervention population (that which receives a programme) and a non- intervention population (that which does not receive a programme) may provide evidence that a particular program has caused a change in nutritional status. The intervention population is the population that receives a program, and the noninter- vention group is similar population that does not receive the program.
Undertaking a nutrition survey provides an ideal opportunity for agencies to learn more about the population they are assist- ing or planning to assist. When undertak- ing a nutrition assessment, it may be use- ful to collect additional information on the population, such as mortality, immuniza- tion and nutrition programme coverage data. Objectives related to these health outcomes should be included in the list of survey objectives. Such objectives could include
• Estimating the coverage of feeding pro- grams;
• Estimating mortality rates (crude and under-5 years); and
• Estimating the coverage of measles vaccination and vitamin A supplemen- tation.
You must decide in which area the survey should be conducted, and you must define this area carefully. Remember that the area from which the survey sample is selected is the only area to which your survey results can be generalized. You will not be able to say anything about an area or pop- ulation that was not eligible to be selected for the survey sample.
In most cases, the area chosen will corre- spond to an administrative or government area, such as a district or province. For WFP purposes, sometimes the area chosen for a survey will correspond to areas where WFP is implementing a programme or is investigating the need to implement a programme. The survey ideally should be conducted in an area where the whole population has a similar nutritional situa- tion because the final estimate of the prevalence of malnutrition can be applied only to the entire population from which the sample was selected. It cannot be applied with any statistical precision to any subgroup or sub-area within the sur- vey population or area. If you conduct a survey in an area in which different groups have very different nutritional statuses, the results will be an average of these different nutritional statuses. For example, if some provinces in a particular nation have suf- fered drought and crop failure while others have not, it would not be very useful to do a nationwide survey to determine which provinces are in greatest need of assis- tance. The result of such a survey would produce only an average measure for the entire nation.