01 / THE IDEA
What does it mean?
Task success rate is successful task attempts divided by all attempts, expressed as a percentage. Define success consistently before observing people. It measures a specific task under specific conditions, not the quality of every outcome in the product.
02 / IN PRACTICE
Make it concrete.
Illustrative example: Ask 20 people to find and book a train ticket for Friday. If 11 complete the booking correctly, the task success rate is 55%.
03 / WHAT TO WATCH FOR
A common mistake.
Counting clicks or search-result views as successful completion.
04 / WHEN IT HELPS
When should you use it?
When evaluating whether a workflow helps users achieve a well-defined goal.
05 / FURTHER READING
Explore the source.
Nielsen Norman Group — Success Rate ↗This is a reference for further learning, not an endorsement or a verbatim quotation.