This is how to calculate d-prime in R. This function takes a data frame called data and returns a d-prime score for each unique entry in the subject column of the data frame. Note that the function will return Inf or -Inf if any value in Hrate or Frate is 1 or 0. This happens whenever someone responds correctly or incorrectly on all the trials.
dprime <- function(data) {
yes <- subset(data, resp=="Y")
no <- subset(data, resp=="N")
hit <- subset(data, resp=="Y" & acc == 1)
falsealarm <- subset(data, resp=="N" & acc == 0)
Hrate <- xtabs(~subject, data=hit)/xtabs(~subject, data=yes)
Frate <- xtabs(~subject, data=falsealarm)/xtabs(~subject, data=no)
dprime_score <- qnorm(Hrate) - qnorm(Frate)
return(dprime_score)
}
A simple usage example:
> data
subject resp acc
1 1 Y 0
2 1 Y 1
3 1 Y 1
4 1 N 0
5 1 N 1
6 2 Y 1
7 2 N 1
8 2 Y 0
9 2 Y 1
10 2 N 0
> dprime(data)
subject
1 2
0.4307273 0.4307273
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