[R] ROC for threshold value, biometrics
Frank E Harrell Jr
f.harrell at vanderbilt.edu
Fri Jun 11 17:06:10 CEST 2004
myint.tin-tin-htar at jvr.ap-hop-paris.fr wrote:
> I am just a beginner of R 1.9.0.
> I try to construct a predictive score for the development of liver
> cancer in cirrhotic patients. So dependant variable is binanry (cancer
> yes or no). Independant variables are biological data. The aim is to
> find out a cut-off value which differentiate (theoratically) from
> normal to pathological state for each biological data.
A binary endpoing is not a good choice for this problem, as the time to
diagnosis is very important. Unless you only have a biopsy at a single
fixed time (e.g., 5 years post study entry) it would be good to consider
for example a Cox proportional hazards model. And there are many
reasons for not using a cutoff, as detailed in my book Regression
> How can I step in procedue to get a cut-off value (threshold) for each
> variable? I think I should try by ROC. But I'm not sure. If so, someone
> can lead me?
Besides not recommending the use of cutoffs on an overall predicted
value, I think that using cutoffs based on separate analyses of
predictors is even worse.
> If not, someone can advice me how ?
> Any advice will be cordially aprreciated.
> Tin Tin Htar Myint
> Research assistant
> Liver unit
> Jean Verdier Hospital, Bondy
> R-help at stat.math.ethz.ch mailing list
> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Frank E Harrell Jr Professor and Chair School of Medicine
Department of Biostatistics Vanderbilt University
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