There are three main practical obstacles to using evidence on the economic impacts of IP… Much of the data needed to develop empirical evidence on copyright and designs is privately held. It enters the public domain chiefly in the form of “evidence” supporting the arguments of lobbyists (“lobbynomics”) rather than as independently verified research conclusions.
My own experience in dissecting IP developments supports this view. It is surprisingly difficult to find “hard data” about copyright piracy, leaving any “debate” to a shouting match between proponents of bald assertions.
We need better data, and we all need to be more circumspect (and humble) before drawing sweeping conclusions from the little that is available.