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