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Risk-adjusted sequential probability ratio tests: applications to Bristol, Shipman and adult cardiac surgery
David Spiegelhalter1, Olivia Grigg, Robin Kinsman
1MRC Biostatistics Unit, Institute of Public Health, Cambridge, UK.
Objective:
To investigate the use of the risk-adjusted sequential probability ratio test in monitoring the cumulative occurrence of adverse clinical outcomes.
Design:
Retrospective analysis of three longitudinal datasets.
Subjects:
Patients aged 65 years and over under the care of Harold Shipman between 1979 and 1997, patients under 1 year of age undergoing paediatric heart surgery in Bristol Royal Infirmary between 1984 and 1995, adult patients receiving cardiac surgery from a team of cardiac surgeons in London,UK.
Main Outcome Measure:
Annual and 30-day mortality rates.
Results:
Using reasonable boundaries, the procedure could have indicated an 'alarm' in Bristol after publication of the 1991 Cardiac Surgical Register, and in 1985 or 1997 for Harold Shipman depending on the data source and the comparator. The cardiac surgeons showed no significant deviation from expected performance.
Conclusions:
The risk-adjusted sequential probability test is simple to implement, can be applied in a variety of contexts, and might have been useful to detect specific instances of past divergent performance. The use of this and related techniques deserves further attention in the context of prospectively monitoring adverse clinical outcomes.