5.14 Mean Time to Complete Task
Limiting the number of UTCs or failing to control for user types will have a negative effect on the
credibility of this metric.
18.5.15 Understandability (Communicativeness) Metrics
Collect the following data for each UTC:
??? % of time spent using the ???help??? system
??? % of time spent consulting a manual
??? % of time spent asking for help from the administrator
??? % score from an UTC product assessment questionnaire
Measure each as a proportion of the total time spent using the product. Identify and eliminate outliers.
Get the mean for the product and compare it with other products or releases. This will answer two
questions:
1. How easy is the product to understand? (Any score of above 30% is ???not very.???)
2. Has understandability improved since the last release? (Compare the two scores.)
Beware of using too few UTCs. This could skew your results.
18.5.16 Learnability Metrics
Collect the following data for each UTC:
??? Initial training time (ITT)
??? Subsequent training time (relearnability) for some gap in use (STT)
??? Score for UTC??™s ability (pre- and post-training) (UTCS)
You need to control for many factors:
??? A UTC (and everyone else) forgets, so test their ability to remember.
??? Some people have longer gaps between system use than others, so allow for this. There are statistics
showing the ability to forget over time, from psychology books.
??? A well-designed system will have visual clues which aid retention.
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