Update on Ratios of Patients to Qualified Nurses

News Blog readers may know that there is a considerable literature on nursing skill mix and patient outcomes in hospital. One of the most important studies is Paul Shekelle’s masterful systematic review from 2013.[1] Taken in the round, the literature shows a consistent association between the ratio of skilled nurses to patients and improved outcomes. A recent large cross-sectional study from a number of European countries reaches similar conclusions [2]; many outcomes of hospital care (including death rates) were improved in association with high levels of qualified nurses. Mortality reduction in hospitals with a favourable ratio of qualified nurses to patients were about 10% lower than in those with a less favourable ratio. An interesting question relates to what nurses do that could make such a large difference. An obvious mediating factor would be vigilance in recording vital signs and responding appropriately to signs of deteriorating physiology. Managing new technology, such as infusion equipment, may also be important. Getting the right medicine into the right patient at the right time is yet a further way good nursing could improve outcomes. Improved ratios are also strongly associated with patient satisfaction. Reassurance and tender care may mediate better physical outcomes given the close interplay between the nervous and immune systems.[3] These, and other, causal pathways are represented in the figure.

086 DCi - Update on Patient to Qualified Nurse Ratios

The above study did not look at process variables that might mediate a beneficial impact on nursing time. However, given  plausible mechanisms by which nurses may improve outcomes and consistent, albeit non-experimental, evidence it is not unreasonable to conclude that improving the ratio of qualified nurses to patients will improve care. Saving money by skill substitution is therefore likely to be a false economy since health economic models are sensitive to quite modest reductions in adverse events.[4]

 — Richard Lilford, CLAHRC WM Director


  1. Shekelle PG. Nurse-patient ratios as a patient safety strategy: a systematic review. Ann Intern Med. 2013; 158(5 Pt 2): 404-9.
  2. 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. 2017; 26(7): 559-68.
  3. Lilford RJ. Brain Activity and Heart Disease – a New Mechanism. NIHR CLAHRC West Midlands News Blog. 9 June 2017.
  4. Lilford RJ, Chilton PJ, Hemming K, Girling AJ, Taylor CA, Barach P. Evaluating policy and service interventions: framework to guide selection and interpretation of study end points. BMJ. 2010; 341: c4413.

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