Nurse staffing and patient safety in acute hospitals: Cassandra calls again?

The risk of adverse patient outcomes,including death, is lower in hospitals thatprovide more registered nurses to carefor patients on inpatient wards. The association has been demonstrated in a bodyof evidence comprising several hundredstudies, involving hundreds of hospitals andmillions of patients from around the world.The association has been shown at hospitallevel in large cross-sectional studies and ina growing number of longitudinal studiesexamining the effect of variation in staffingexperienced by individuals.1–3 In the contextof such an extensive body of evidence, onemight ask what could possibly be left todiscover?