What’s New in the Patient Safety World

January 2017

Nursing Skill Mix and Patient Safety



Studies have generally shown that higher nurse:patient ratios are associated with better quality of care and lower mortality rates. But the number of nurses is not the only important factor. Nursing skill mix is another consideration.


A recent study from European hospitals participating in the RN4CAST Consortium looked at the relationship between hospital nursing skill mix and quality of care, mortality, and patient ratings (Aiken 2016). They found that every 10-point increase in the percentage of professional nurses among all nursing personnel was associated with lower odds of mortality (OR=0.89), lower odds of low hospital ratings from patients (OR=0.90) and lower odds of reports of poor quality (OR=0.89), poor safety grades (OR=0.85) and other poor outcomes (0.80<OR<0.93), after adjusting for patient and hospital factors. Each 10 percentage point reduction in the proportion of professional nurses is associated with an 11% increase in the odds of death.


In a commentary (Needleman 2016) on the Aiken study, Needleman notes that previous studies from Canada and the US have also shown lower nursing skill mix to be associated with higher rates of adverse events and longer lengths of stay. Needleman in a previous study (Needleman 2006) had shown that greater use of RNs in preference to LPNs appears to reduce in-hospital patient deaths and pay for itself.


These studies, of course, fly in the face of recent trends to replace RN’s with less skilled levels of nursing care in attempt to reduce hospital costs. Such reductions in higher level nursing staff may paradoxically (because of increased adverse events and longer lengths of stay) increase hospital costs.


A 2015 review of the literature on nursing case mix (Jacob 2015) found that economic savings from substituting registered nurses with other health professionals may be offset by increased patient length of stay in hospital and increased patient mortality.


Some studies have suggested that differences in the importance of skill mix may differ between medical and surgical admissions. Li and colleagues, using data on both nursing staffing and nurse skill mix at the unit, rather than hospital, level (Li 2011) found that for medical admissions, a business case could be made for improving nurse staffing by increasing the proportion of RN hours while holding total nursing hours unchanged.


Ironically, almost the same day that the Aiken study was published a news article was published on the development of a nurse robot through collaboration between Duke’s School of Engineering and School of Nursing (Bridges 2016). But don’t worry- it’s not intended to replace nurses! Rather it is being developed to assist nurses and other healthcare workers in certain environments. The example given in the article is assisting in the care of an Ebola patient.


We’d like to add one other consideration. In our multiple columns on the “weekend” or “after hours” effect we’ve pointed out the numerous non-nursing tasks that nurses end up doing. The roles of clerical staff, housekeeping staff, transport staff, etc. are not accounted for in the nursing skill mix formulas in studies done to date. We think that in addition to maintaining good nurse:patient ratios and high levels of nursing skill mix you need to ensure that nurses have time to attend to clinical tasks and not be burdened by non-clinical tasks.






Aiken LH, Sloane D, Griffiths P, et al. Nursing skill mix in European hospitals: cross-sectional study of the association with mortality, patient ratings, and quality of care

BMJ Qual Saf 2016; Published Online First 15 November 2016




Needleman J. Nursing skill mix and patient outcomes (Editorial). BMJ Qual Saf 2016; December 30, 2016




Needleman J, Buerhaus PI, Stewart M, et al. Nurse staffing in hospitals: is there a business case for quality? Health Aff (Millwood) 2006; 25: 204-211




Jacob ER, McKenna L, D'Amore A. The changing skill mix in nursing: considerations for and against different levels of nurse. J Nurs Manag 2015; 23: 421-426




Li Y-F, Wong ES, Sales AE, et al. Nurse staffing and patient care costs in acute inpatient nursing units. Med Care 2011; 49: 708-715




Bridges V. Duke officials test, refine robot-nurse. The News & Observer (North Carolina) 2016; November 16, 2016







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