I got an e-mail from Rafe Donahue a couple of months ago with two plots that I couldn't get to display properly, and so time passed, time passed, but I am now having another shot at it, including also Rafe's comments:
...logistic regression allows one to predict a categorical outcome as a function of other variables. The output is typically a cumulative logit (log-odds), which is linear, but those are hard to understand. So I drew the probabilities and their confidence intervals.
So, you can see that as your TAC score goes up, you are less likely to be in the No Disease group, and if you have a TAC score of about 10,000 you have about a 50-50 chance of being in the Rutherford 1,2,3 club (disease) or the Rutherford 4,5,6 club (very bad disease).
I did the analysis in SAS and drew the plot in R.
Also is a plot that shows how to predict TAC score from disease group. This one shows the means, confidence intervals for the means, and prediction intervals for the individual scores.
Meanwhile Rafe has sent another e-mail with his thoughts on the study of biostatistics, it's not all cool plots was the gist, I know, I know, I know . . .