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  • anna williams thinks this is interesting:

Performance metrics are not the magical elixir for every situation. Similar to other metrics, an adequate sample size is required. Although the statistics will work whether you have 2 or 100 users, your confidence level will change dramatically depending on the sample size. If you’re only concerned about identifying the lowest of the low-hanging fruit, such as identifying only the most severe problems with a product, performance metrics are probably not a good use of time or money. But if you need a more fine-grained evaluation and have the time to collect data from 10 or more users, you should be able to derive meaningful performance metrics with reasonable confidence levels.

From

Cover of Measuring the User Experience, 2nd Edition

Note

DAWSON REPORT - can calculate range in comparison to optimal time on task