What is the ideal nursing skill mix?
Discussion around staffing frequently focuses on numbers of staff.
The research found that the average proportion of registered nursing staff - compared to unregistered healthcare assistants - on day shifts was 56%.
Dame Christine Beasley, the previous chief nursing officer for England, has previously said the ratio of nurses to assistants should not fall below 60:40.
The research found the proportion of registered nurses to assistants varied from 43% to 68% between trusts.