Methods
The search strategy was guided by the following research questions: (a) Does RN staffing affect the cost of care delivered to patients in acute hospital settings? and (b) Does RN staffing affect patient LOS? The data search included five electronic databases (Medline, CINAHL, Health star, Cochrane, ABI/Inform), and manual searching from reference lists of key articles. The search strategy and search terms are provided in Table 1 .
Studies relevant to the research questions were included if they met the following six criteria: published between 1990 and 2006; focused on nurse staffing and length of stay or costs; relevant to care of all patients; peer-reviewed; use of correlational, experimental, retrospective or observation methodologies allowing for a degree of generalizability; and description of the designs and method of data collection to test the relationship between registered nurse staffing, length of stay, and hospital costs. Studies in nursing homes or that examined other health workforce characteristics, such as medical staff ratios or partnership between nurses and staff in other disciplines, were excluded