The application of current lifetable methods to compare cystic fibrosis median survival internationally is limited

Background: Comparing international estimates of survival can be a useful way of highlighting differences in life expectancy between cystic fibrosis (CF) populations. In this study, we compared survival in two CF populations. Methods: The current lifetable method takes age-specific mortality rates observed in a given year and applies them to a hypothetical population assuming those rates will remain the same in the future. This was used to compare median predicted survival in the United States (US) and the Republic of Ireland (RoI) (1986-2008). Median age at death among decedents was also examined. Results: In both countries, median age at death was lower than median predicted survival. Successive increases in annual median predicted survival were not observed; rather an overall improvement was discerned over time. In the RoI, where absolute numbers of deaths were small, year-on-year fluctuations in age-specific mortality rates resulted in wide-ranging annual median predicted survival estimates. Conclusion: Median age at death is not a good measure of CF survival. Though median predicted survival improved in each country over the study period, between-country comparison at a given time point may be misleading for rare disorders like CF. Longitudinal outcomes must be examined.