Figure 2.

Probability of death in the National Emphysema Treatment Trial. Kaplan-Meier estimates of the cumulative probability of death as a function of years after randomization to lung volume reduction surgery (LVRS) (gray line) or medical treatment (black line) for (A) all patients and (B) upper lobe–predominant and low baseline exercise capacity subgroup. The P value is from the Fisher's exact test for difference in the proportions of patients who died during the 4.3 years (median) of follow-up. Shown below each graph are the numbers of patients at risk, the Kaplan-Meier probabilities, the ratio of the probabilities (LVRS:medical), and P value for the difference in these probabilities. Reprinted by permission from Reference 3.