Power for effectiveness outcomes
Power estimations simplistically assume the TEACH intervention will improve ventilator-free days among some percentage of surviving patients within an institution who would have been extubated within 28 days by a single day, compared to baseline-phase ventilator-free days at that same center. We assume no TEACH-related improvement in mortality rates or proportion of patients not extubated by day 27. At control sites, we assume no improvement in ventilator-free day distributions from baseline levels.Simulations were carried out using final baseline data (with simulated post-intervention data obtained by resampling from each institution’s baseline cohort and then modifying ventilator-free days when appropriate due to modelled TEACH effect) and projected enrollment numbers for the 3 years of the intervention phase. Conservatively, a level of ventilator-free day “granularity” achieving satisfactory model convergence in effectively 100% of simulations was used. From these simulations, estimated power to detect a significant TEACH effect is approximately 87% if TEACH improves ventilator-free days by 1 day (compared to the usual care intervention) among two-thirds of surviving patients ventilator-free within 28 days of intubation. Estimated power is reduced to 51% if this one ventilator-free day improvement occurs among only one-half of such surviving patients.