[R] ROCR - best sensitivity/specificity tradeoff?

[David Winsemius]

On Apr 6, 2011, at 2:27 PM, Christian Meesters wrote:

> Hi,
>
> 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 perhaps in your learning phase regarding decision theory perhaps?  
You have not indicated that you understand the need to assign a cost  
to errors of either type before you can talk about a preferred cutoff  
value.


> Or do I need an entirely different approach for this? Or is there an  
> alternative solution?
>
> Thanks,
> Christian

-- 

David Winsemius, MD
West Hartford, CT