Sales A, Sharp N, Li YF, Lowy E, Greiner G, Liu CF, Alt-White A, Rick C, Sochalski J, Mitchell PH, Rosenthal G, Stetler C, Cournoyer P, Needleman J. The association between nursing factors and patient mortality in the Veterans Health Administration: the view from the nursing unit level. Med Care. 2008 Sep; 46(9):938-45.