Calculating an intervention's (cost-)effectiveness for the real-world target population: The potential of combining strengths of both RCTs and observational data

Economic evaluations most often use results from randomised controlled trials (RCTs) to model effectiveness. Inconsiderate application of the absolute treatment effect from RCTs may result in unrealistic estimates of an intervention's benefit for the real-world target population. The baseline risk of events in this target population may differ significantly from the baseline risk in the RCT population.An approach to handle this problem is to combine observational data with evidence from RCTs. Reliable administrative or register data can provide an estimate of the real-world baseline risks. In combination with the relative treatment effect from well-performed RCTs this results in an estimate of the absolute benefit for the relevant target population. Applying this approach, one must remain cautious about the validity of the assumption of a constant relative treatment effect.