About 12 or 13 years ago a Lufthansa led survey by a German university looked at in house data from the company pilots regarding the last time they suffered confusion/error/incident. Lufthansa made it err, rewarding to take part. Approx. 3000 responses came in.
University came up with a pretty standard pie chart of incident analysis but they also added a new chunk of pie - Technical/Human which I suspect ties in with Alf's observations. It proved a sizeable chunk but with a single airline group looked at not huge numbers.
Rob