Epidemiologists, who are accustomed to using systematic and quantitative approaches, have come to play an important role in the evaluation of public health services and other activities. Evaluation is the process of determining, as systematically and objectively as possible, the relevance, effectiveness, efficiency, and impact of activities with respect to established goals.
Effectiveness refers to the ability of a program to produce the intended or expected results in the field; effectiveness differs from efficacy, which is the ability to produce results under ideal conditions.
Efficiency refers to the ability of the program to produce the intendedresults with a minimum expenditure of time and resources.
The evaluation itself may focus on plans (formative evaluation), operations (process evaluation), impact (summative evaluation), or outcomes — or any combination of these. Evaluation of an immunization program, for example, might assess the efficiency of the operations, the proportion of the target population immunized, and the apparent impact of the program on the incidence of vaccine-preventable diseases. Similarly, the evaluation of a surveillance system might address the operations and attributes of the system, its ability to detect cases or outbreaks, and its usefulness.