DNA Examiners: Judgment and Influence

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DNA analysis is widely believed to offer objective and accurate evidence in legal cases. But, like other forensic methods, DNA analysis requires human judgment. Such judgment may be influenced by non-forensic contextual information. An important and as yet unstudied issue is whether a DNA examiner's decision about how to test an object for DNA depends on contextual cues such as comments made by police investigators. If so, this raises questions about (a) whether such cues can affect whether an examiner finds DNA on an object, (b) how examiners respond to challenges pertaining to the testing choices they make, and (c) how jurors weigh DNA evidence following such challenges. This research includes two controlled experimental studies. In Study 1, one hundred experienced DNA examiners will receive materials from a simulated criminal case in which their expectations about where DNA evidence likely exists on an object is manipulated via contextual cues. The examiners will then perform a DNA analysis and provide conclusions. Next, the examiners' will respond to cross-exam-like questions that challenge their testing decisions and conclusions. Study 2 examines how mock jurors' judgments and decisions about a case are affected by (a) the complexity of arguments raised on the DNA examiner's cross-exam, and (b) the examiner's response to those arguments.This research has significant implications for the criminal justice system, for the practice of forensic science, and for the advancement of psychological theory. The criminal justice system benefits from identifying, and then correcting for, factors that can interfere with forensic decision-making. These improvements, which may find their way into forensic science training programs and protocols, can help convict the guilty and free the innocent. This research also advances psychological theory by providing insight into how and when cognitive and motivational biases operate in a complex, multi-stage, multi-person decision task.