Patients with cystic fibrosis (CF), their families, carers, insurers, health care planners, and CF carriers all have an interest in knowing the lifespan of people with the disease. Evidence-based medicine is now explicitly practised by many clinicians in their everyday clinical work. This practice should include prognosis,1 where the expected lifespan is the most important statistic.

However, clinicians with a responsibility for these patients are faced with a large literature on the survival of people with CF, which presents a contradictory picture. My purpose is to show how these contradictions may be resolved by reference to other published material. I have examined three “notable” observations to show what inferences may be reasonably drawn from them concerning the lifespan of people with CF.

In the absence of properly conducted randomised controlled clinical trials, observational methods have been used to try to determine the relative efficacy of different models of providing clinical care, even though such studies provide only weak evidence.2 In particular, the possible advantage of care at specialist centres compared to care by local paediatricians has been debated for many years. Because of the relatively small numbers of cases and local variations in the care delivered, international comparisons have been used to assess these two different strategies for care.