Pennsylvania remains the largest U.S. state without a tax on natural gas production, thanks in part to a study released under the banner of the Pennsylvania State University. The 2009 report predicted drillers would shun Pennsylvania if new taxes were imposed, and lawmakers cited it the following year when they rejected a 5 percent tax proposed by then-Governor Ed Rendell. What the study didn't do was note that it was sponsored by gas drillers and led by an economist with a history of producing industry-friendly research on economic and energy issues. As the U.S. enjoys a natural-gas boom from a process called hydraulic fracturing, or fracking, producers are taking a page from the tobacco industry playbook: funding research at established universities that arrives at conclusions that counter concerns raised by critics. Cary Nelson, president of the American Association of University Professors, who made the tobacco analogy, said companies and their trade associations are buying the prestige" of universities that are sometimes not transparent about funding nor vigilant enough to prevent financial interests from shaping research findings. The Penn State report is not the only example. A professor at the University of Texas at Austin led a February study that found no evidence of ground-water contamination from fracking. He did not reveal that he is a member of the board of a gas producer. Company filings examined by Bloomberg indicate that in 2011, he received more than $400,000 in compensation from the company, which has fracking operations in Texas.