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Program data have substantial limitations:
- Most program data do not include population estimates. As a result, in order to calculate coverage, the number of persons in the population of interest must be obtained elsewhere.
- Most programmes do not record information on health impact. The indicators measured by program data do not directly measure the health status of the population. Rather, they give some indication of intermediate variables, such as the delivery of services. For interventions for which the efficacy is well demonstrated, such as vaccination or oral rehydration, measuring coverage is sufficient to conclude the presence of a health impact. For other interventions, measurement of health impact may be more necessary.
- "Service provided" does not mean "Service accessed". Many barriers may inhibit people's ability to use the service even if it is available. For example, if latrines are grouped in one corner of the camp, far away from much of the population, they may not be used. Non-food items, like blankets, bednets, or cookware, may be sold by recipients or hoarded by some members of the community. For these reasons, a survey often gives better information on "true" coverage.