Michigan's three largest public universities surpassed $2 billion in combined annual research and development spending, and together have created 600,000 alumni earning nearly one-sixth of all wage and salary income in the state, a new economic impact report finds. The report, to be released today from East Lansing-based Anderson Economic Group LLC, found total R&D spending grew about $100 million in the 2010-11 academic year from a year earlier and more than $631 million since the 2006-07 academic year. In 2011, it exceeded $2 billion for the first time. The corridor, an alliance of the University of Michigan, Michigan State University and Wayne State University, also had a combined direct and indirect impact of $15.5 billion on Michigan's economy, $2.6 billion more than four years earlier, the report said. In addition, just under 600,000 of their alumni earned about $29 billion in income that year, of which $5.2 billion was "incremental" income gained over and above what they would presumably earn without their education.