Handling over-dispersion of performance indicators. Issue 5 (29th September 2005)

• Record Type: Journal Article
• Authors: Spiegelhalter, D J
• Is Part Of: Quality & safety in health care. Volume 14:Issue 5(2005)
• Page Start: 347
• Page End: 351
• Publication Date: 2005-09-29
• Subjects: over-dispersion -- risk stratification -- random effects model -- performance indicators
• DOI: 10.1136/qshc.2005.013755
• Languages: English
• ISSNs: 1475-3898

Abstract

Abstract : Objectives: A problem can arise when a performance indicator shows substantially more variability than would be expected by chance alone, since ignoring such "over-dispersion" could lead to a large number of institutions being inappropriately classified as "abnormal". A number of options for handling this phenomenon are investigated, ranging from improved risk stratification to fitting a statistical model that robustly estimates the degree of over-dispersion. Design: Retrospective analysis of publicly available data on survival following coronary artery bypass grafts, emergency readmission rates, and teenage pregnancies. Setting: NHS trusts in England. Results: Funnel plots clearly show the influence of the method chosen for dealing with over-dispersion on the "banding" a trust receives. Both multiplicative and additive approaches are feasible and give intuitively reasonable results, but the additive random effects formulation appears to have a stronger conceptual foundation. Conclusion: A random effects model may offer a reasonable solution. This method has now been adopted by the UK Healthcare Commission in their derivation of star ratings.