Multiple reviews of research have established that higher registered nurse staffing levels in hospitals are associated with better patient outcomes and improved care quality, including lower risks of in-hospital mortality, shorter lengths of stay and fewer omissions of necessary care. However, beyond providing an injunction to invest in ‘more’ staff, such studies rarely indicate directly how many staff are required. The ability to determine the ‘right’ number of staff, both to employ and to deploy on any given shift, is an imperative from the perspective of both quality and efficiency of care .