A realist logic model of the links between nurse staffing and the outcomes of nursing

Background: There has been a long-standing debate over the definition and nature of the quality of healthcare and factors that influence and enhance quality. Within nursing, the challenge is to identify the outcomes that are measurable and amenable to change as a result of nursing care. Arising originally from concerns over potential nurse staffing shortages and nurse retention within the United States, an extensive literature has developed in the acute sector, exploring nurse staffing and its consequences. All of these studies raise the generic question of what potential causal mechanisms might link nurse staffing levels and skill mix to issues of patient safety and outcome. Objectives: To generate a tentative logic model to understand existing findings and to elucidate possible ways in which nurse staffing and skill mix may affect patient and nurse outcomes. Methods: This study was grounded within the principles of realist evaluation, realist review and logic modelling. The existing literature was reviewed to bring to light the underlying rationale suggested by the authors of this study on how nursing care might affect patient outcomes. A stepby- step process was followed to demonstrate the generation of a tentative logic model of how nurse staffing might influence patient, and nursing, outcomes. Results: The final logic model depicts staffing adequacy as having a complex link with patient outcomes. This is mediated at a general level through factors in the process of care (for example,nurse surveillance, clinical judgement, level of education, level of nurse training and length of nursing experience) and tasks left undone. These operate in conjunction with working with other nurses who are clinically competent, having good nurse-physician relationships and communication, supportive nurse manager/supervisor and good teamwork. Conclusions: This study extends the understanding of the mechanisms through which nurse staffing levels may result in adverse patient outcomes in the acute sector. Key intervening variables are the application of nurse intuition, operation of clinical judgement and missed nursing care/ tasks left undone. The tentative logic model can be used to draw up areas and hypotheses to guide the direction of future research and to aid interpretation of existing research.