Statistical evaluation of ventilator-free days as an efficacy measure in clinical trials of treatments for acute respiratory distress syndrome

Use of ventilator-free days as a trial end point allows smaller sample sizes if it is assumed that the treatment being tested simultaneously reduces the duration of ventilation and improves mortality. It is unlikely that a treatment that led to higher mortality could lead to a statistically significant improvement in ventilator-free days. This would be especially true if the treatment were also required to produce a nominal improvement in mortality.