I’m suspicious of reports that give a precise dollar figure for how much value an industry contributes to the economy — especially when the results help the industry to make a case for some legislation it wants passed. Numbers always sound so authoritative, even though economists often privately acknowledge that so many assumptions go into a measurement of an industry’s impact that the results can be little more than a collection of educated guesses. Still, it’s interesting to see the number that the International Intellectual Property Alliance came out with today showing how much of the economy comes from copyright industries — including film, TV, music, computer software, and publishing. They accounted for $931.8B, or 6.4%, of the gross domestic product in 2010, the group says based on findings from Stephen Siwek of Economists Incorporated, who relied on government data. If you throw in other industries that benefit from copyrighted work, then the economic value rises to $1.627T, or 11.1% of GDP. The core businesses also employed 5.1M U.S. workers, or 4.8% of the private sector, with wages averaging $78,128, 27% more than the U.S. average. The data show that we need “strong and modern copyright laws that take into account changes in technology and the continuing harm caused by copyright theft,” IIPA counsel Steven Metalitz says. Not surprisingly, several members of the alliance — including the MPAA and Recording Industry Association of America — support controversial bills in Congress that would empower the government to block overseas websites that traffic in pirated content.