Back in 2008, the USA passed a new federal law called the PRO-IP Act (Prioritizing Resources and Organization for Intellectual Property Act). One of the things this law did was increase the penalties for counterfeiting and copyright infringement.
But one of the lesser but still important parts of this law was where it ordered the GAO (General Accounting Office, a federal agency) to conduct a review of existing piracy statistics. The GAO was also supposed to try to accurately measure the effect of piracy. Today the GAO issued their report. You can download it here.
The report doesn't actually come out and say that the statistics are bunk. But it does discredit the loss estimates that are supposed to have come from the US gov't. are figments of someone's imagination. This report also discusses the validity of industry estimates. It doesn't disprove them, though.