Re: identification test procedure ("Timothy C. Justus" )

Subject: Re: identification test procedure
From:    "Timothy C. Justus"  <Timothy.C.Justus(at)DARTMOUTH.EDU>
Date:    Fri, 9 Oct 1998 12:46:06 EDT

Hello - In response to James Beauchamp's message, I would suggest that a signal detection analysis be applied to determine if subjects can tell the difference between the real and synthesized tones. The problem with only knowing the subject's correct answers (hit rate) is that it doesn't allow you to separate sensitivity (the ability to discriminate) from decision criteria. By knowing both the hit rate and the false alarm rate (or the miss and correct rejection rates, since these are 1 minus the other two, respectively) you can plot a receiver operating characteristic (ROC) which can separate effects of sensitivity and decision criterion. The probability of hits is plotted against the probability of false alarms. A point falling near the diagonal would represent chance performance - they can't tell the difference - whereas points away from this line show discrimination. You can draw ROC curves on these figures representing a given level of discrimination, with points along the same curve represent different decision criteria. I'm sure there are individuals out there who could explain this much better than I. I hope this is helpful. Timothy Justus Dartmouth College McGill is running a new version of LISTSERV (1.8d on Windows NT). Information is available on the WEB at

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