Statistical Analysis
The trial was designed to detect an absolute difference of 3.5 percentage points in the survival rates between the two study groups, with the use of a two-sided alpha level of 0.05 and a power of 80%. To compare the distribution of characteristics and outcomes for the two types of CPR instruction, we used the chi-square statistic for categorical variables and the independent-samples t-test or the nonparametric Mann–Whitney U test for continuous variables. Primary comparisons were performed according to randomization status. We also performed an efficacy analysis restricted to cases in which bystander CPR progressed to chest compression as a consequence of dispatcher instructions. Because one site was unable to assess neurologic status at discharge, we present the overall results as well as results restricted to the two sites that were able to ascertain neurologic status.