[R] Calculate Specificity and Sensitivity for a given threshold value

[Kaliss]

Hi list,


I'm new to R and I'm currently using ROCR package.
Data in input look like this:

DIAGNOSIS	SCORE
1	0.387945
1	0.50405
1	0.435667
1	0.358057
1	0.583512
1	0.387945
1	0.531795
1	0.527148
0	0.526397
0	0.372935
1	0.861097

And I run the following simple code:
d <- read.table("inputFile", header=TRUE);
pred <- prediction(d$SCORE, d$DIAGNOSIS);
perf <- performance( pred, "tpr", "fpr");
plot(perf)

So building the curve works easily.
My question is: can I have the specificity and the sensitivity for
a score threshold = 0.5 (for example)? How do I compute this ? 

Thank you in advance
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