ROC analysis: different results using SPSS and MedCalc

#1
Hi!

I am analyzing a group of patients for which I have the values of a certain test variable X and their survival (1 or 0). I want to perform a ROC analysis and get the AUC value, and the optimal criterion by which I can divide the patients into surviving/non-surviving. The optimal criterion should correspond to the maximum pair of sensitivity and specificity (which should also correspond to the Youden index).
When I perform the ROC analysis I get different results for the optimal criterion in MedCalc and in SPSS and I am wondering why this analysis is so dependent on the software I use. Since in MedCalc the optimal criterion is calculated by the Youden index, I wrote a code in SPSS to calculate this index, but, as I said, the results are different.
Could you please help me to understand where the problem is?

In case, please let me know if you need for information. I can provide the raw data if it is needed.

I use Windows 7, IBM SPSS Statistics version 20 and MedCalc version 14.

Thank you very much for your help!