It is unclear whether training for nursing assistants was equivalent in all countries studied. In England, the Department of Health plans to introduce "nursing associates", who would have 18 months' training and work alongside professional nurses and existing, less well-trained health care assistants.

Additionally, the study does not prove that more qualified nurses are the reason for the differences in death rates and quality of care. The research is based on one "snapshot" of what was happening in hospitals at one point in time (2009 to 2010). Other factors, such as local doctor staffing levels, may also have an effect on outcomes.