Do we need all the components of the research excellence framework?

The Research Excellence Framework (REF) is underpinned by three areas of assessment: outputs, impact and environment. However, discussing the findings of their recent research Mehmet Pinar and Tim Horne argue that these elements correlate to the extent that assessing all of them is largely inefficient. If this is the case, they pose the question: is it time to eliminate one of these elements in the next REF cycle?