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4.4.3 Efficiency as a Combination of Task Success and Time

Another view of efficiency is that it’s a combination of two of the metrics discussed in this chapter: task success and time on task. The Common Industry Format for Usability Test Reports (ISO/IEC 25062:2006) specifies that the “core measure of efficiency” is the ratio of the task completion rate to the mean time per task. Basically, it expresses task success per unit time.

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