We found no effect of schedule ( 24 - , 16 - or 12-h shifts ) on adverse events ( 81.3 , 76.3 and 78.2 events per 1000 patient-days , respectively ; p = 0.7 ) or on residents ' sleepiness in the daytime ( mean rating 2.33 , 2.61 and 2.30 , respectively ; p = 0.3 ) or at night ( mean rating 3.06 , 2.73 and 2.42 , respectively ; p = 0.2 ) .