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3.5 Reliability of experimental results 59

35
Mouse
Number of targets selected per minute 25
Touchscreen
30

20

15

10
Novice Experienced
FIGURE 3.6
Interaction effects.

device when the interaction is normally brief and the opportunities for training are
limited, such as an ATM interface. In contrast, a mouse might be more appropriate
for long-term, frequent tasks, such as interacting with a computer desktop.

3.5 RELIABILITY OF EXPERIMENTAL RESULTS
All experimental research strives for high reliability. Reliable experiments can be
replicated by other research teams in other locations and yield results that are con-
sistent, dependable, and stable. One big challenge in HCI studies is that in contrast
to the “hard sciences,” such as physics, chemistry, and biology, measurements of hu-
man behavior and social interaction are normally subject to higher fluctuations and,
therefore, are less replicable. The fluctuations in experimental results are referred to
as errors.

3.5.1 RANDOM ERRORS
We may observe a participant typing several text documents during five sessions
and obtain an actual typing speed of 50 words per minute. It is very unlikely that we
would get the same typing speed for all five sessions. Instead, we may end up with
data like this:
Session 1: 46 words per minute
Session 2: 52 words per minute
Session 3: 47 words per minute
Session 4: 51 words per minute
Session 5: 53 words per minute