Abstract:Different understanding of the nature of validity leads to diverse validity theory and validation practice The positivistic paradigm focuses on certainty and generalization The naturalistic paradigm emphasizes the degree to which the evaluator and evaluation audience can agree on, and feel confident about, an interpretation of the evaluation findings The challenges of validity research are: reliability and validity, the unitary and the divisible, and validity and validation, etc The key notion is that although it is clear that important differences remain between positivistic and naturalistic perspectives on validity, validity is establishing what counts as evidence We have seen that the criteria for doing this can differ depending on the research perspective being used