Every practice environment today is concerned with nurse staffing and patient safety, which have become concerns globally and in every type of practice setting. While research has provided evidence that the number and type of nurses in a given setting is important for the delivery of high-quality health care, critical questions still remain. Framing nurse staffing in terms more specific than minimum ratios or care requirements based on minutes or hours of direct care required is difficult. While these may be necessary variables, most would agree they are not sufficient for matching nurse as resource with the highly variable needs of patients. The question of how many nurses are needed? can be approached from a macro or a micro perspective. At the macro level, key insights are available, at least when examining numbers of nurses in comparison to other types of health workers. A recent report from the World Health Organization (2006) analyzes the relationship of the health workforce to key health outcomes across countries. Several key outcome indicators, such as immunization rates or newborn birth weights, are directly related to the density or proportion of various types of health care workers to the population. Data indicate that the proportion of nurses to population is a better determinant than the density of physicians on many key outcome variables. While this may seem intuitive to us in nursing, data have not been available in the past that demonstrate this striking relationship to this degree. It provides an important next step toward looking at specific health workforce interventions to address health needs in a global context. At the micro level, several empirical insights have been reported in recent years. The work by Aiken, Clarke, Sloane, Sochalski, and Silber (2002) indicates that in hospitals with high patient-to-nurse ratios, risk-adjusted mortality and failure-to- rescue rates are higher in surgical patients. This research has frequently been used to support the mandated or minimum staffing ratios in some states in the United States and in many acute care settings as well. The study provides a metric for the strength of the relationship of nurse staffing levels and their effect on patient outcomes, but it does not provide the type of insight or understanding we would like to have to guide specific staffing decisions. The relationships among total hours of nursing care, nursing skill mix, and adverse patient outcomes have also been examined at the level of the nursing care unit. Blegen, Goode, and Reed (1998) looked at a variety of adverse outcomes including unit rates of medication errors, patient falls, skin breakdown, infections, and family complaints. They found that the proportion of hours of care delivered by registered nurses was inversely related to the unit rates of medication errors, patient complaints, and decubiti. They also found unexpectedly that the relationship between the proportion of care provided by registered nurses and the total hours of care from all nursing personnel, including both RN and assistive personnel, was curvilinear; as the proportion provided by registered nurses increased, rates of adverse outcomes decreased up to 87. …