Table 2

Results of the regression analysis

Baseline characteristicCoefficient (SE)
QALY loss with TKRQALY loss without TKRTotal costs with TKR (£)
Male0.056 (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 30.414 (0.067)*0.227 (0.087)*492 (208)*
Constant1.712 (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.