Introduction - Measuring the User Experience: Collecting, Analyzing, and Presenting Usability Metrics - page 7

reliable way of doing it. An inch is the same length regardless of who is mea-
suring it, and a second lasts for the same amount of time no matter what the
time-keeping device is. Standards for such measures are defined by a society as a
whole and are based on standard definitions of each measure.
Metrics exist in many areas of our lives. We're familiar with many metrics, such as
time, distance, weight, height, speed, temperature, and volume. Every industry, activ-
ity, and culture has its own set of metrics. For example, the auto industry is interested
in the horsepower of a car, its gas mileage, and the cost of materials. The computer
industry is concerned with processor speed, memory size, and power requirements.
At home, we're interested in similar measurements: how our weight changes when
we step on the bathroom scale, where to set our thermostat in the evening, and how
to interpret our water bill every month.
The user experience field is no different. We have a set of metrics specific to
our profession: task success, user satisfaction, and errors, among others. This
topic gathers all the UX metrics in one place and explains how to use these met-
rics to provide maximum benefit to you and your organization.
So what is a UX metric and how does it compare to other types of metrics? Like
all other metrics, UX metrics are based on a reliable system of measurement: Using
the same set of measurements each time something is measured should result in
comparable outcomes. All UX metrics must be observable in some way, either directly
or indirectly. This observation might be simply noting that a task was completed suc-
cessfully or noting the time required to complete the task. All UX metrics must be
quantifiable —they have to be turned into a number or counted in some way. All UX
metrics also require that the thing being measured represents some aspect of the user
experience, presented in a numeric format. For example, a UX metric might reveal
that90%oftheusersareabletocompleteasetoftasksinlessthan1minuteor50%
of users failed to notice a key element on the interface.
What makes a UX metric different from other metrics? UX metrics reveal
something about the user experience—about the personal experience of the
human being using a product or system. A UX metric reveals something about
the interaction between the user and the product: some aspect of effectiveness
(being able to complete a task), efficiency (the amount of effort required to com-
plete the task), or satisfaction (the degree to which the user was happy with his or
her experience while performing the task).
Another difference between UX metrics and other metrics is that they mea-
sure something about people and their behavior or attitudes. Because people are
amazingly diverse and adaptable, we sometimes encounter challenges in our UX
metrics. For this reason, we discuss confidence intervals with most of the UX met-
rics discussed in order to reflect the variability in the data. We will also discuss
what metrics we consider relevant (and less relevant) in a UX context.
Certain things are not considered UX metrics, such as overall preferences and
attitudes not tied to an actual experience of using something. Think of some