My criminal procedure professor evaluates wrongful conviction rates for the Wall Street Journal. The best evidence puts the wrongful conviction rate for serious felonies at 2.3% to 3.3% (one source says 7% but it has far too small a sample size to be reliable). He points out clear statistical goofs of Oregon prosecutor Joshua Marquis (.027%) and Colorado District Judge Morris B. Hoffman (.065%).
Is 96.7% to 97.7% good enough? Maybe not: "If as few as 1% of criminal convictions are erroneous, right now there are more than 20,000 innocent defendants behind bars."