StATS: Using APR-DRGs for risk adjustment (May 24, 2006).

The 3M company, famous for Post-It notes, among other things, has a division for health information systems. One of their products is software that produces classifications called "All patient Refined Diagnosis Related Groups" or APR-DRGs. These APR-DRGs are computed from information typically collected as part of the billing process. Patients in a common APR-DRG represent a reasonably homogenous set of patients with respect to type of condition and severity of disease.

This product has both financial and research applications. In the research realm, you might want to define a narrow group of patients with a reasonably homogenous risk profile. This would allow you to use stratification or matching on the APR-DRG so as to improve the precision of the findings.

You might also have an observational study where you know that there are some imbalances with respect to prognostic factors. You could use the APR-DRG as a covariate to insure that any differences in risk are adjusted for in the analysis.

There is an increasing demand for "report cards" for physicians and hospitals that will allow patients to make informed decisions about where they get their health care from. These report cards need careful adjustment for risk levels, because there is a well established tendency for the better individuals and groups to get referrals for the more complex and difficult patients. If you don't perform an appropriate risk adjustment, you end up seeing the worst outcomes among the very best groups and individuals.

I hesitate to recommend commercial products, because most researchers are starving for funding, but this product looks pretty good. I had to use it for a research study a while back, and may end up using it again.

The 3M Health Information System group has a web page at

and the description of the APR-DRG system is at

Here's an example of a publication that examines APR-DRGs and shows that this grouping can account for about 16% of the variation in length of stay.

This page was written by Steve Simon while working at Children's Mercy Hospital. Although I do not hold the copyright for this material, I am reproducing it here as a service, as it is no longer available on the Children's Mercy Hospital website. Need more information? I have a page with general help resources. You can also browse for pages similar to this one at Category: Covariate adjustment.