Background The British National Health Service (NHS) employs a large number of individuals, at great monetary cost, to provide direct care to patients. Changes in the combinations of staff, including nurses, nurse practitioners and midwives, delivering this care have been shown to be effective in many settings.

Findings The (opportunity) cost implications of such changes in the skill mix are rarely evaluated adequately. The impact of releasing professionals’ time has not been estimated and therefore determining whether changes are cost-effective is difficult; these difficulties have often been increased by poor study design.

Conclusions Economic evaluation has been under-utilized in studies of skill mix. If economic evaluation demonstrates that skill mix changes reduce cost and improve or maintain patient outcomes, this is strong evidence that these changes should be implemented. Incentives may be required to attract the necessary personnel. This in itself may influence the cost of changing the skill mix and therefore the situation should be monitored as both costs and effectiveness can alter over time.