[Risk adjustment in external quality assurance with multivariate analysis].

Surgical clinics throughout Germany are under political and economical pressure. Comparing outcomes across clinics or ranking become more and more popular although there are no generally accepted and scientifically valid methods how to compare. Using original data of the external quality assurance project of the chamber of physicians of Westfalia-Lippia it is shown in this article that comparing raw data is often misleading. Differences in risk factors (case mix) have to be taken into consideration. A model using logistic regression methods to adjust for case mix in legality and morbidity of hip fractures is proposed. A ranking list before and after adjusting for risk factors shows partly dramatic changes. One clinic for example changed from position 97 (out of one hundred) to position 26.