Incremental evaluation sets periods of evaluation for distance education programs. During these periods, evaluators collect program data and analyze it. This type of evaluation is practical and has the benefit of being able to use methods of evaluation for traditional education. It's much like the evaluation of traditional education programs.
Formative evaluation's purpose is to improve the learning process. Data is collected during the distance learning program's design and development. The evaluation happens before the program is fully established, so formative evaluation allows these programs to improve their systems before they're solidified.
Summative and formative evaluations are nearly mutually exclusive. When using summative evaluation, evaluators analyze the cumulative effect of the distance learning program. The evaluators observe the program's end result and compare it to the program's stated goals.
Distance learning evaluation can also take the form of case studies, where evaluators limit themselves to reviewing an individual distance learning program. The program isn't studied. Instead, evaluators analyze a program's audience or students and generalize the results to distance learning. For example, a case study might follow a newly established educational television program's audience and chart their improvement. These results would help determine the program's funding level and method of teaching.