Program evaluation is but one of many tools of legislative oversight. Other tools include performance audits, executive agency plans and testimony, budget studies and documentation, and special legislative staff studies. Patton emphasizes that evaluation ought to be useful to decision making and lead to program improvement. Program evaluation generally differs from traditional audit approaches as it focuses upon programs, not organizational units. As such, it views the program as a whole system, even if it cuts across agency lines.
Program evaluation emphasizes measurement of outputs and impacts as well as inputs and processes.
It is concerned not only with whether a program is efficiently managed, but also with whether it is achieving its intended purposes. It also focuses on the reasons why programs are successful or failing. Knowing the underlying causes enables policy makers to consider alternative approaches to correct deficiencies or improve results. Finally, program evaluation involves extensive data collection and data analyses and sometimes even establishing appropriate benchmarks for measurement of the program's results. Thus, the evaluative tasks will require expertise and care in developing and presenting data and analyses and will involve and necessitate the cooperation of the Executive Branch agencies under review.