External and internal validity

Internal validity

• is the extent to which the costs and benefits are unbiased. To assess internal validity we have to look closely at the quality of the design and analysis of the study.

Users should ask themselves the question: are the methods employed in the study appropriate and the results valid?

External validity

• addresses whether the analysis is applicable to different patient groups and settings. External validity is usually explored through the application of modelling and/or sensivity analysis, to investiage how much the results will be affected by changes in costs/benefits that may arise in different settings.

Users should ask themselves the question: if the results are internally valid, would they apply to my setting?