Hi everybody,
Pascal, your code works, but when I want to do the graph I have an error
message.
here is my code :
x<-rev(unlist(pred@cutoffs))
tpf<-unlist(performance(pred, "tpr")@y.values)
fpf<-unlist(performance(pred,"fpr")@y.values)
ll<-length(x)
p<-(tpf[1:(ll-1)]-tpf[2:ll])/(fpf[1:(ll-1)]-fp
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 th
Hi,
I made a mistake, effectively Pascal your method given to the first message
is correct. I didn't use the good data, so it's sure that it could not work
!
But, I have an another question : Can I obtain a same graph except that the
y-axis represents the likelihood ratio ?
All the best,
Camill
Hi,
Pascal, I tried to use your method which functions but the values of the
abscissa are not good. When I talked about “value”, I wanted mean the values
of my starting dataset that I have classified into two classes positive and
negative classes, such as this :
Value Status TPF TN
Hi everybody,
I have a data set with a value and a status (positive or negative case) and
I want make a ROC Analysis. So, with ROCR Package, I have got the ROC curve
(True Positive Fraction [tpf] according 1-True Negative Fraction [1-tnf]).
http://r.789695.n4.nabble.com/file/n4469203/01.png
But
Eleni Christodoulou wrote:
> Richard, thanks, I think it will work. I will calculate the cutoff value
> and then, from the prediction object, find the fpr that is related to it and
> put it as argument to performance. I will keep you informed.
>
> Eleni
You will probably need to bootstrap the en
Richard, thanks, I think it will work. I will calculate the cutoff value
and then, from the prediction object, find the fpr that is related to it and
put it as argument to performance. I will keep you informed.
Eleni
On Wed, Mar 19, 2008 at 11:51 AM, Richard Pearson <
[EMAIL PROTECTED]> wrote:
Eleni
Does the fpr.stop argument do what you want? This is described in
?performance under the details of the "auc" measure. Try, e.g.
perform=performance(pred,measure="auc",fpr.stop=0.5)
Richard.
Eleni Christodoulou wrote:
> Hello list,
>
> I am trying to perform ROC analysis and count the
Hello list,
I am trying to perform ROC analysis and count the AUC in order to validate
my results. I use package ROCR. I would like to count the AUC not under the
cutoff found by "performance" but to use another cutoff that I calculate.
How could I change the following command in order to get wha
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