Surgical clinics throughout Germany are under political and economical pres
sure. Comparing outcomes across clinics or ranking become more and more pop
ular although there are no generally accepted and scientifically valid meth
ods how to compare.
Using original data of the external quality assurance project of the chambe
r of physicians of Westphalia-Lippia it is shown in this article that compa
ring raw data is often misleading. Differences in risk factors (case mix) h
ave to be taken into consideration.
A model using logistic regression methods to adjust for case mix in letalit
y and morbidity of hip fractures is proposed. A ranking list before and aft
er adjusting for risk factors shows partly dramatic changes. One clinic for
example changed from position 97 (out of one hundred) to position 26.