• risk model
• risk stratification
• coronary surgery

Coronary bypass surgery is perhaps the most investigated surgical procedure¹ with clear end points for outcome such as operative mortality. Consequently, it has long been regarded as a sentinel operation for outcome.^2,3 Over 25 000 coronary bypass operations are performed per year in the UK and the operative mortality has reached a plateau in recent years of approximately 3%. The risk that an individual patient will not survive surgery depends on many factors, some of which can be quantified and form the basis of risk scoring systems.

Several risk stratification systems have developed over recent years with varying complexity, including those based on simple additive models such as Parsonnet,⁴ EuroSCORE^5–7 and others.^8,9 More complex statistical algorithms using logistic regression^10,11 and Bayes modelling⁸ also exist. The ideal model should have high …