Box 2Relationship between FEV₁% and survival reported by Tappenden 2013

“On the basis of this review, it is reasonable to suggest that there exists Level 1/2 evidence to support the hypothesis that a change in FEV₁% directly leads to a change in mortality, and therefore FEV₁% alone is unlikely to represent a valid independent surrogate for patient survival. As such, the assumption of a direct linear relationship between FEV₁% alone and mortality risk, without adjustment for other confounding factors, as assumed within the Forest Laboratories analysis, should be approached with considerable caution…

On the basis of the weaknesses in the evidence associated with the potential relationship between FEV₁% and mortality (see Methodological issues surrounding the economic evaluation of cystic fibrosis treatments), this relationship was not considered within the Assessment Group model.”