Dr. Michael Byrne:

The short answer is that I do not know. It would be a function of policy objectives for the sector, so there would not be a level that would apply across sectors. If, for example, you regarded growth in the private rental sector as a policy target, there might be one number; however, if the policy were more focused on growing home ownership and social housing, another figure might be regarded as appropriate.

In the short term, in the absence of significant research that could investigate this, it would be ideal to develop a benchmark based on the number of exits over a period. This would at least allow you to assess what constituted an unusually high or low number of exits, etc., so you could at least get a picture of how the private rental market behaves over a period and the levels that are more typical of the market. Ideally, you would go significantly beyond that and gain a better understanding.