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and determine that the elapsed time was 18 minutes, how to get Excel to calculate that
isn't so obvious. Internally, Excel stores all times as a number reflecting the number of
seconds elapsed since midnight. So to convert an Excel time to minutes, multiply it by
60 (the number of minutes in an hour) and then by 24 (the number of hours in a day).
To convert to seconds, multiply by another 60 (the number of seconds in a minute).
Here's what it looks like in Excel, including the formula:
4.2.3 Analyzing and Presenting Time-on-Task Data
You can analyze and present time-on-task data in many different ways. Perhaps
the most common way is to look at the average amount of time spent on any par-
ticular task or set of tasks by averaging all the times for each user by task ( Figure
4.4 ). This is a straightforward and intuitive way to report time-on-task data. One
downside is the potential variability across users. For example, if you have several
users who took an exceedingly long time to complete a task, it may increase the
average considerably. Therefore, you should always report a confidence interval
to show the variability in the time data. This will not only show the variability
within the same task but also help visualize the difference across tasks to deter-
mine whether there is a statistically significant difference between tasks.
Mean Time per Task (seconds)
(Error bars represent the 90% confidence interval)
60
50
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10
0
Task
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Task
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Task
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Task
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Figure 4.4 Mean time on task, in seconds, for 19 tasks. Error bars represent a 90% confidence interval.
These data are from an online study of a prototype website.
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