[R] ROCR - best sensitivity/specificity tradeoff?

[Claudia Beleites]

Christian,

> My questions concerns the ROCR package and I hope somebody here on
> the list can help - or point me to some better place.
>
> When evaluating a model's performane, like this:
>
>
> pred1<- predict(model, ..., type="response") pred2<-
> prediction(pred1, binary_classifier_vector) perf<- performance(pred,
> "sens", "spec")
>
> (Where "prediction" and "performance" are ROCR-functions.)
>
> How can I then retrieve the cutoff value for the
> sensitivity/specificity tradeoff with regard to the data in the model
> (e.g. model = glm(binary_classifier_vector ~ data, family="binomial",
> data=some_dataset)? Perhaps I missed something in the manual? Or do I
> need an entirely different approach for this? Or is there an
> alternative solution?

a) look into the performance object, you find all values there

b) have a look at this thread
https://stat.ethz.ch/pipermail/r-help/attachments/20100523/51ec813f/attachment.pl
http://finzi.psych.upenn.edu/Rhelp10/2010-May/240021.html
http://finzi.psych.upenn.edu/Rhelp10/2010-May/240043.html

Claudia