Time on task calculator
Paste task times in seconds or minutes:seconds. Get the geometric mean with a confidence interval, the median and the usual descriptive statistics, as recommended for skewed task-time data.
Free and private: everything is calculated in your browser and nothing you paste is sent anywhere.
How it is calculated
- Task times are positively skewed: a few slow participants pull the arithmetic mean up. Taking logs makes the data roughly symmetric.
- The geometric mean is the exponent of the mean of the log times. The confidence interval is calculated on the log scale with the t distribution and transformed back, so it is not symmetric.
- Sauro and Lewis (2010) found the geometric mean to be the best estimate of the median task time for samples under about 25. For larger samples the median works well.
Frequently asked questions
Should I report the mean or the median task time?
For usability tests with fewer than about 25 participants, report the geometric mean. It estimates the population median better than either the sample median or the arithmetic mean (Sauro & Lewis, 2010). With larger samples the median is fine.
How do I calculate a geometric mean?
Take the natural log of each time, average the logs, then raise e to that average. This calculator does it for you and also gives a confidence interval.
Should I include failed tasks?
It depends on your question. Times for successful attempts only describe how long the task takes when it works. Including failures mixes in time spent struggling or giving up. Whichever you choose, say so in your report.