Results of the regression analysis
| Baseline characteristic | Coefficient (SE) | ||
| QALY loss with TKR† | QALY loss without TKR† | Total costs with TKR (£) | |
| Male | 0.056 (0.065) | −0.001 (0.054) | 593 (181)* |
| Age at operation (years) | 0.007 (0.003)* | 0.002 (0.004) | −8 (12) |
| Pre-operative OKS | −0.040 (0.004)* | −0.087 (0.004)* | −52 (12)* |
| ASA grade 3 | 0.414 (0.067)* | 0.227 (0.087)* | 492 (208)* |
| Constant | 1.712 (0.201)* | 4.274 (0.325)* | 8573 (881)* |
The incremental cost-effectiveness ratio (expressed as cost per QALY) for any given patient equals: (male×593—age×8—OKS×52 + ASA grade 3×492 + 8573)/((male×−0.001 + age×0.002—OKS×0.087+ ASA grade 3×0.227+4.274)—(male×0.056 + age×0.007—OKS×0.040+ ASA grade 3×0.414+1.712)). Costs and quality-adjusted life years (QALYs) were discounted at 3.5% per annum.
*p<0.05.
↵† QALY loss indicates the number of discounted QALYs that would have been accrued if patients had experienced an EQ-5D utility of 1 for 5 years (4.67 QALYs) minus the number of discounted QALYs that the patient actually experienced.
ASA, American Society of Anaesthesiologists classification (1=completely fit and healthy, 2=some illness but no effect on daily activity, 3=symptomatic illness with minimal restriction on life); OKS, Oxford Knee Score (new scoring system running from zero (severe problems on all functions) to 48 (no problems))41; QALY, quality-adjusted life year; TKR, total knee replacement.