What test to compare a mean mortality score of a group to observed death rate ?

[Venki]

I have 1000 patients divided into 3 groups depending upon the predictive mortality rate for patients. This predictive score was calculated based upon baseline risk profile of the patient.

3 groups are as follows:

Low risk group: those patients who have predictive mortality rate of 0 to 1.5%

Intermediate risk group: >1.5% - 3%

High risk group: >3%

So, I will have a mean±SD for the predictive mortality rate for each group.

In each of the 3 group: I have the "real" observed death rate as well. 

I was wondering how best to compare the predictive score in each group to the observed death rate in each group? What kind of test should I do?