On 01/30/2012 08:52 PM, Josiane NJIWA wrote:


Hello all,

I am very new to R and i am facing two problems. First i didn't succeed 
changing the konsole language in english even after trying the line command set 
language='en'.
I would like to plot ROC curves. I have a serie of 10 threshold tests that i do 
for 10 patients. The prediction for the patients is always the same but the 
status can change given to the considered threshold.
I have 11 columns of 10 rows, the first colums containing the10 lines of the 
predicted status of the patients (0=cured, 1=non cured). Then follow 10 columns 
(10 thresholds) containing the found status using the threshold.
Please do someone know how i can use those values with R to plot ROC curves?

Hi Josiane,
The function roc.from.table in the "epicalc" package will produce a basic ROC curve. You will have to get the table that you send to the function in the correct form. I think you will have to lay out the table like this:

        Predicted       Above threshold
Threshold1      x               x
Threshold2      x               x
Threshold3      x               x
Threshold4      x               x
Threshold5      x               x
Threshold6      x               x
Threshold7      x               x
Threshold8      x               x
Threshold9      x               x
Threshold10     x               x

I may be quite wrong as I don't know exactly what the successive threshold values may mean. You will probably want to run the function with grid=FALSE.

Jim

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