Control chart displaying the number of unplanned extubations in the pre-improvement (A) and post-improvement phases (B). Before improvement, there were 3.8 unplanned extubations/100 intubated days (A). After improvement, there were 2.7 unplanned extubations/100 intubated days (B). Tests were performed with unequal sample sizes. Mean P = .02. Dashed lines indicate upper and lower control limits.