Variation in outcome and ranking of hospitals: An analysis from the Swedish knee arthroplasty register

Background Hospital-specific variation in outcome is generally considered to be an important source of information for clinical improvement. We have measured the magnitude of this variation.

Methods We determined the revision risk in 37,642 cemented primary total knee arthroplasties inserted as a result of osteoarthritis from 1993 through 2002 at 93 hospitals in Sweden. We used 2 essentially different methods to estimate risk of revision: a fixed-effects model (Cox’s proportional hazards model) and a random-effects model (shared gamma frailty model).

Results The 2 models ranked hospitals differently. As expected, the fixed-effects model provided more dispersed estimates of hospital-specific revision rates. In contrast to the random-effects model, chance events can easily cause overly optimistic or pessimistic outcomes in the fixed-effects model. Although the revision risk varied significantly between hospitals, the overall revision risk was still low.

Interpretation Assessment of variation in outcome is an important instrument in the continuing effort to improve clinical care. However, regarding revision rate after knee arthroplasty, we do not believe that such analyses necessarily provide valid information on the current quality of care. We question their value as information source for seeking personal healthcare.