Despite copious opinions, data on this topic are limited and largely based on observational studies and/or the use of before vs after designs that use potentially problematic historical controls.34 Among 824 patients in an ICU in the United Kingdom, the standardized hospital mortality ratio declined from 1.11 to 0.81 after changing to the 24/7 staffing model.35 A US study of 4,388 patients in a medical ICU found that such a change was not associated with improved ICU mortality (10.2% vs 10.4%, P = .83), hospital mortality (17% vs 19%, P = .33), ICU LOS (difference, −0.2 days; P = .08) or family satisfaction, although improvements occurred in ICU-acquired complications, processes of care, hospital LOS, and intensivist burnout.36 Notably, in this latter study the standard staffing model had ICU fellows present overnight. The only interventional study that did not use historical control subjects37 used an alternating crossover study design in two closed-model, intensivist-run ICUs, one academic and one in a community hospital without house staff. Including the community ICU was valuable because it is more comparable to most ICUs than are the large, academic units that are the subject of most ICU research.14,38 In this study, 24/7 intensivist presence did not improve patient outcomes or family satisfaction in either ICU. The main effect of the shiftwork model was on the intensivists, who reported reduced job and life stresses. The largest study thus far was a retrospective, cross-sectional analysis of 49 ICUs participating in the Acute Physiology and Chronic Health Evaluation (APACHE) database project.39 Nocturnal intensivist presence was associated with lower hospital mortality in ICUs in which daytime involvement of intensivists was low intensity (OR, 0.62; P = .04) but not in ICUs in which daytime intensivist involvement was high intensity (OR, 1.08; P = .78).