[R] ROC Analysis

[Camille Leclerc]

Hi everybody,

Pascal, your script works again but I want to calculate the LR otherwise.
I know the likelihood ratio is linked at the roc curve and so there are
different ways to calculate the LR.
The slope of an ROC curve can be defined in three ways:
(1) as the tangent at a particular point on the ROC curve corresponding to a
test value x
(2) as the slope between the origin 0 and the point on the ROC curve
corresponding to a test value x 
(3) as the slope between two points on the ROC curve corresponding to the
test values x and y

http://r.789695.n4.nabble.com/file/n4478233/LR.png 

But in my case, I want calculated the LR with the third way. 
So, LR (x,y) =(sensitivity (x)-sensitivity (y))/(specificity (y)-specificity
(x))
                    = (TPR(x)-TPR (y))/(FPR (x)-FPR (y))

It is possible ?!

All the best,
Camille


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Camille Leclerc, Master student
Lab ESE, UMR CNRS 8079
Univ Paris-Sud
Bat 362
F-91405  Orsay Cedex FRANCE
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