Override rate — the oversight vital sign
If human in the loop is the control, override rate is how you check its pulse.
A rate near zero has two readings, one fine and one not: either the model is genuinely excellent, or the humans have stopped looking — automation bias, alert fatigue, or a workflow where disagreeing is expensive. A very high rate also has two readings: a model performing badly, or one performing fine on a population it was never meant for. The metric cannot distinguish these alone; its job is to raise the question, which is why it belongs on the monitoring dashboard next to the performance metrics rather than in an annual report.
The governance move is to trend it per model, ask for an explanation at the extremes, and record the answer — one more line in the monitoring evidence a surveyor can date.
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