In order to improve the health status of their populations, most countries are developing their ability to provide primary health care. This relies upon a capacity to manage the national health system which, in turn, is dependent upon information for purposes of planning, supervision and monitoring of health activities. Data are required to define the need for health services, the efficiency of existing services, as well as their impact on morbidity and mortality.

Although much of the necessary information can be obtained from routine sources, some can best be obtained through the use of surveys. The World Health Organization (WHO) and other international agencies have been active in promoting the use of such surveys. As an example, through its Expanded Programme on Immunization (EPI), WHO aims to ensure the availability of immunization for all the children of the world by the year 1990. This effort is considered a vital step towards the attainment of WHO's stated goal of health for all by the year 2000.

The impact of diseases such as neonatal tetanus, poliomyelitis, measles, whooping cough, diphtheria and tuberculosis upon children in the developing world is compounded by the fact that many of these children are severely weakened by malnutrition and repeated episodes of diarrhoea and malaria. Immunization programmes are seen as an important measure for reducing infant and childhood disability and deaths, which act as spurs to sustain high birth rates.

A major need of the EPI has been an appropriate system for gathering information. Reliable data are necessary to document the level of morbidity and mortality from specific target diseases as well as the level of immunization coverage against these diseases. Since this information is not readily available to health managers in many developing countries, EPI has worked to develop a method which could obtain accurate information quickly and cheaply. A method was sought which, in addition, could be implemented in a relatively standardized manner from one country to the next. This would permit training materials and operation manuals to be developed for widespread use, and would facilitate comparison of results between countries. In addition, standardized methodology makes possible the comparison from one time period to another within a particular country, which is needed to measure the impact of the immunization programme's efforts over time.

The primary purpose of the methodology developed by EPI was to assess the level of immunization coverage. Because of the operational success of this methodology, it has been adopted for a range of other purposes including assessments of population morbidity due to specific causes, service coverage and health service needs. h is the purpose of this article to review the EPI methodology, to consider its suitability for other purposes, and to suggest limitations, modifications and alternatives to meet the needs of different health programmes.