Fig. 2.

Significant determinants of the net-health-benefit (NHB) of lumbar spinal fusion (adjusted for age, gender, diagnosis, duration of pain, smoking habits, severity of disability, emotional distress, surgical technique, and number of levels fused where relevant). Curves are average NHB as a function of willingness-to-pay with 95% bias-corrected, bootstrapped CI (dotted curves). The vertical dotted grey line is the willingness-to-pay accepted today. a The influence of secondary degeneration is associated with significantly lower NHB compared with primary degeneration, however, this influence becomes insignificant with increasing values of willingness-to-pay. b The influence of smoking is relatively constant over willingness-to-pay; smoking significantly lowers the NHB (in comparison with no smoking). c The influence of pre-operative disability is slightly increasing for increasing values of willingness-to-pay; severe disability is associated with higher NHB (in comparison with moderate or intermediate disability). d The influence of pre-operative emotional distress is slightly increasing with increasing values of willingness-to-pay; emotional distress is associated with higher NHB (in comparison with no emotional distress)