• A review of the evidence to define the nursing contribution to patient outcome is presented. The review relies on work related to nursing sensitive outcomes, skill mix and changing roles.
• Methodological difficulties associated with these studies are highlighted.
• Areas requiring further research are discussed.
• It is suggested that experimental evidence is not always appropriate, when attempting to describe nursing activity. The authors advocate that new methodologies, in particular practitioner-centred research, are needed to unpack the nature of nursing.