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Error rate 0:52
A 52-second explainer of Error rate, narrated over the same demo you can try yourself.
Try the interactive Error rate demo
What this video covers
Error rate is how often people make errors while doing a task - mistakes per attempt, or the share of attempts that go wrong. It's a usability signal, not a verdict on users, and it has many causes: design, task complexity, training, environment, unfamiliarity or who you tested. A cluster of the same error is worth investigating, and the type of error hints at the kind of fix.
When one in three attempts goes wrong, the instinct is "users aren't paying attention" - but if a third of people trip on the same step, the step tripped them. Error rate turns that into a number you can't argue with, and the type of error - a fumbled tap versus a misunderstood label - points straight at whether you've got an interface problem or a comprehension one.
