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Single-Issue Testing
By definition, single-issue testing uses relevant questions that cover only one event. Because most polygraph techniques use between two and four relevant questions, each of the relevant questions would be a rewording of one central question. For example, for a single-issue technique with three relevant questions used to solve a bank robbery, they might be worded like this: Did you rob the ABC Bank last Thursday; Last Thursday did you rob the ABC bank on Main Street, and; Are you the one who robbed the ABC Bank last week?
Laboratory research investigating the accuracy of single-issue polygraph examinations has found a median accuracy of 86%. Field research suggests a slightly higher at 89%. Higher accuracy is associated with valid testing and scoring protocols, whereas lower accuracy tends to reflect departures from standard field practices.
Even with advancements in sensors and computers, there is little optimism of large increases in polygraph decision accuracy. However, as a diagnostic tool, the single-issue polygraph test fairs well against diagnostic methods in other fields. By way of comparison, single-issue polygraph decision accuracy is lower than decision accuracy when diagnosing appendicitis with ultrasound, but equivalent to the accuracy of diagnoses made for breast cancer using either ultrasound or MRI. Polygraph decisions are higher than the standard tools used by psychologists to diagnose personality disorders or depression.
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