1- Historical study: Is the community improving?
We can decide only by comparing experience (rates) over time, because it is well known that the health and disease pattern in communities never constant. There are fluctuations both over short and long periods of time. e.g. old disease small pox, new ones legionnaires disease, Lassa fever, AIDS.
2. Community diagnosis: What are the health problems?
Community diagnosis generally refers to the identification and quantification of health problems in a community in terms of mortality and morbidity rates and ratios.
By quantification of health problems we lay down priorities in disease control and prevention.
The quantification of health problems can be a source of new knowledge about distributions, and prevention.
3. Planning and evaluation: Planning is essential for rational use of the limited resources. Epidemiological information about the distribution of health problems over time and place provides the fundamental basis for planning and developing the needed health services and for assessing the impact of these services on the people's problems. Any measures taken to control or prevent a disease must be followed by an evaluation .