Curious about the political leanings of people who read classic science fiction authors? Check out this online excerpt from the 1977 Analog Yearbook. It sums up the politics of 70s scifi readers in a handy graph.
Authors William Sims Bainbridge and Murray M Dalziel also group authors by subgenre, and offers this handy way to figure out which authors you'll like based on others whose work you already enjoy.
Check out a detailed explanation of their research at Mister Bainbridge's site.