For readability, we had a decision of either using a poor proxy and possibly making a decision based on it, or simply acknowledging that this is a point that cannot currently be measured. Ultimately, we decided not to capture this as a quantitative measure, though we did ask engineers to self-rate their code quality.
You could teach someone incorrectly how to tie a knot, swing a good club, or bake a cake — teaching them bad technique that does more harm than good — yet if you survey them, they will probably self-rate their skill higher.
I think you can do better — that's not to say it's necessarily worth it: ask 5 people to rate the readability of code of the engineers. Don't ask them, "How would you rate the Readability of it?" but "How would you rate how easy it was to understand and maintain?"
