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Case‐mix adjustment for evaluation of mortality in cystic fibrosis *

Comparison of patient mortality rates in cystic fibrosis (CF) obtained from different institutions requires the use of case‐mix adjustment methods to account for baseline differences in patient and disease characteristics. There is no current professional consensus on the use of case‐mix adjustment methods for use in comparing mortality rates in CF. Characteristics used for this case‐mix adjustment should include those that are different across institutions and are associated with patient survival. They should not include characteristics of disease severity that may be a consequence of effectiveness of treatment. The goal of these analyses was to identify a set of these characteristics of patients or disease that would be useful for case‐mix adjustment of CF mortality rates. Data from the Cystic Fibrosis Foundation Patient Registry and from the United States Census of the Population (1990) were used in these analyses. Kaplan‐Meier techniques, the log‐rank test, and Cox proportional hazards regression were used to estimate survivorship, calculate hazard ratios (HR), 95% confidence intervals (CI95%), and to conduct tests of statistical significance.