[R] no true negative data, need roc curve

[Jessica Streicher]

Above mentioned formula is wrong - maybe a typo
http://en.wikipedia.org/wiki/Receiver_operating_characteristic

The false positive rate is the rate of false positives, meaning how many of the total negatives (all in reality negatives(N), that is, all negatives falsely classified as positives(fp) and all negatives correctly classified as negatives(tn)) have been falsely classified as positive.

Also the authors obviously had (N+P=number of features), and therefore at least could have computed this properly. For example:

N+P=100
P=TP+FN
N=FP+TN
-> do the math with what you got

On 17.08.2012, at 11:13, vjyns wrote:

> Hi,
> 
>     thanks for the quick response, but as i said in my case due to two
> different threshold the detected features will differ. Moreover, there is
> some standard /refined/ formula in calculating the tpr and fpr. herewith i
> had attached the refined formula from a standard international journal 
> http://r.789695.n4.nabble.com/file/n4640577/tpr_and_fpr.jpg 
> 
> when i used the above mentioned formula (fpr=fp/fp+tp) then i can able to
> see my point are distributed on the extreme left corner. Like this it is
> possible to put all the 6 images.  Will you please suggest me now how to
> obtain the plot for different images of two threshold. 
> 
> 
> 
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