I've a cognitive task that assess working memory. It has 20 trials with 9 trials having a target to which they've to respond by saying "yes". While for the non target trials they don't have to respond.
The test will yield a hit score and two error scores i.e., error of omissions and commissions.
I know I can calculate the hit percentage by dividing the hit score and dividing it by 9. But I am not sure how should I calculate the "false alarm rate" ( error of commission) and the "miss rate" (error of omissions)
Can anyone please help me on this??
Thanks
Vatsal
In this task, using SDT, you can define the trials as follows:
- Target trials to which participants respond "yes" = hits
- Target trials to which participants do not respond = misses
- Non-target trials to which participants respond "yes" = false alarms
- Non-target trials to which participants do not respond = correct rejections
Using the above, you can calculate the following:
Hit Rate = number of hits/(number of hits+ number of misses)
Miss Rate =number of misses/(number of hits+ number of misses)
False Alarm Rate = number of false alarms/(number of false alarms + number of correct rejections).
Correct Rejection Rate = number of correct rejections/(number of false alarms + number of correct rejections).
I hope this helps!
Hi Vatsal,
In your task, a hit would be define as the trials where the target stimulus (signal) was present, and a false alarm as the trials where the participant responded the target stimulus was present when in reality it wasn't. Misses are answers where the signal was present and the participant responded it was absent. Then, like Jessica said:
Hit Rate = number of hits/(number of hits+ number of misses)
Miss Rate =number of misses/(number of hits+ number of misses)
False Alarm Rate = number of false alarms/(number of false alarms + number of correct rejections).
If you want to calculate sensitivity (d') and criterion, you can do the following:
d' = P(Hit) - P(False alarms) (probabilities in Z scores)
Criterion = - (P(Hit) + P(False alarms))/2
Best!
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