A researcher wants to test a teacher-focused intervention in schools. However, she worries that if she randomizes teachers within a school to receive the intervention or not, there may be contamination. She fears that teachers will talk to each other about the study, and that control group teachers will observe intervention teachers' behavior and model it, even though they were not randomized to receive the intervention. In response, the researcher decides to randomize different schools to receive the teacher intervention or no intervention.
Results Eighty-five percent of the 983 study patients met criteria for acute respiratory distress syndrome at enrollment. Tidal volumes remained similar in the 2 groups, and mean positive end-expiratory pressures were (SD, ) cm H 2 O in the experimental group vs (SD, ) cm H 2 O among controls during the first 72 hours ( P < .001). All-cause hospital mortality rates were % and %, respectively (relative risk [RR], ; 95% confidence interval [CI], -; P = .19). Barotrauma rates were % and % (RR, ; 95% CI, -; P = .33). The experimental group had lower rates of refractory hypoxemia (% vs %; RR, ; 95% CI, -; P = .01), death with refractory hypoxemia (% vs %; RR, ; 95% CI, -; P = .03), and previously defined eligible use of rescue therapies (% vs %; RR, ; 95% CI, -; P = .045).