  What don’t we know?   Finally, how should that knowledge, and the limits to it, guide our response to the boom? What do we know about previous booms? I am going to re-use a chart that originated in a research paper by Jonathan Kearns and Christian Gillitzer 1 , with some updating.
This was the basis of a previous address last November 2 . I have noticed it being shown rather more widely of late, no doubt because of the striking messages it conveys.