Table 1.

Nominal rates of human unreliability for generic tasks (after Kirwan [16])

Task	Nominal error rate	95% CI
Completely familiar, well-designed, highly practised routine task	0.0004	0.00008, 0.009
Routine, highly practised, rapid task requiring little skill	0.02	0.007, 0.045
Fairly simple task performed rapidly or given scant attention	0.09	0.06, 0.13
Complex task requiring high level of comprehension and skill	0.16	0.12, 0.28
Totally unfamiliar task, performed at speed, with no real idea of likely consequences	0.55	0.35, 0.97