Most evaluators seem to presume that all evaluative studies should result in conclusive evidence. Often, however, less than conclusive evidence may not only suffice, but be the only real alternative under conditions of limited evaluation resources. Three levels of evidence common to evaluation studies are discussed: suggestive evidence, preponderant evidence, and conclusive evidence. Ten factors are also presented which can be used to determine the level of certainty appropriate for a given evaluation study. Consideration of these factors enables the evaluator to specify when less than conclusive evidence is acceptable. © 1982.
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