A strategy for gathering data for evaluations which involves conducting interviews with selected respondents who are likely to have unique knowledge or insights that can help evaluators assess the impact of a policy or program.
(Brians, Craig Leonard, Lars B. Willnat, Jarol B. Manheim and Richard C. Rich. 2008. Empirical Political Analysis: Quantitative and Qualitative Research Methods, 7th ed. New York: Pearson.)