I am currently looking at continuous data and seeking a correlation with the presence (and severity, ie, normal, mild, moderate, severe) of a disease entity. Now, so far, running Spearman on SPSS, I've gotten an R of 0.370, p<0.001.
I need help on a couple of things. Can/Should I perform a multinomial regression analysis? Also, I'd like to generate a ROC and find out corresponding cut-off values that may pertain to the severity of the disease, i.e., Normal, Mild, Moderate, Severe.
Please advise on how to go about this. Any input is highly appreciated.