1) Participants A and B have the same hit rate (.82), but A has greater sensitivity, as evidenced by a lower false alarm rate (.24 vs. .40). The d' is 1.62 for Participant A, and 1.17 for Participant B. The criterion values for A and B are .71 and .25, respectively. This means that A is more conservative than B, requiring stronger evidence of a signal before indicating that the signal is present.
2) The construction worker probably is malingering. That is, he is pretending to have a greater hearing deficit than he actually does. How do we know this? If he was actually deaf, his hit rate and false alarm rate would be approximately equal, producing d' near zero. His false alarm rate is .50, as would be expected if he was guessing, but his hit rate is .10. These hit and false alarm rates yields a d' value of -1.28.
What this means is that in situations where there was no signal, he was simply guessing (false alarm rate = .50). If he really couldn't hear any of the test stimuli, then his hit rate should also have been around .50. However, his very low hit rate of .10 suggests that when he heard a signal he was more likely to say "no" than "yes" and that produced a negative d' value. We can see from this example that Signal Detection Theory can be used to measure sensitivity to different types of items as well as decision strategies of participants.
3) Using the SDT applet above, create three situations that yield a d' of approximately 1.
a) Hit rate = .85, False Alarm rate = .52
b) False Alarm rate = .40, Hit rate = .77
c) Hit rate = .30, False Alarm rate = .065
Close This Window