Gathering human intelligence via repeated interviewing: further empirical tests of the Scharff technique

Research on investigative interviewing has only recently started to compare the efficacy of different techniques for gathering intelligence from human sources. So far the research has focused exclusively on sources interviewed once, thus overlooking that most sources are interviewed multiple times. The present study attempts to remedy this gap in the literature. Students (N = 66) took on the role of semi-cooperative sources, holding incomplete information about an upcoming terrorist attack. The sources were informed that they would be interviewed at least once, and that additional interviews might follow. Half of the sources were interviewed on three occasions with the Scharff technique (consisting of five tactics), and the other half was interviewed on three occasions using the so-called direct approach (i.e. open-ended and specific questions). Collapsing the outcome over the three interviews, the Scharff technique resulted in significantly more new information compared to the direct approach. Furthermore, sources interviewed by the direct approach overestimated how much new information they had revealed, whereas the sources interviewed by the Scharff technique underestimated their contribution (although not significantly so). The current study advances previous research by further contextualizing the tests of the efficacy of human intelligence gathering techniques.