[R] ROC curve

[Jim Lemon]

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