I think the best data we have of this in the US is the exoneration rate of death penalty convictions, which is startlingly high. A study from 2014 found it to be around 4% (https://www.pnas.org/doi/full/10.1073/pnas.1306417111).

4% may sound low to some, but when people's live are on the line that's terribly high. If a plane had a 4% failure rate it would be considered a colossal failure.