Case Studies - Measuring the User Experience: Collecting, Analyzing, and Presenting Usability Metrics - page 249

Table 10.1 Errors by condition

Mean STD Min Max

Right slap (RS) 6.4 6.689 0 31

Right thumb (RT) 0.663 1.158 0 6

Left slap (LS) 2.911 3.689 0 18

Left thumb (LT)

0.55

1.993 0 14

Total errors 10.50 9.69 0 49

Table 10.1 Errors by condition.
Table 10.2 Error category, condition, and text
Error Category Error Condition Error Text Example

Pressure or angle
that affects the
contrast of an image

More finger area
needs to be in contact
with the scanner

“Press more”
“Lower the angle of your
fingers”

“Not all four fingers are
detected”
“Fingers are spread too
wide. Please place all four
fingers inside the box”

Not all fingers are
detected Detection of fingers

“Move your hand to the
left”
“Move your hand up”

Vertical and horizontal
misalignment

Movement of fingers

“Rotate your hand
clockwise”
“Rotate your thumb
counterclockwise”
“The direction of your
hand is not correct. Please
place four fingers upright
in the center”

Fingers are not
positioned upright Rotation of fingers

Table 10.2 Error category, condition, and text.

are also shown in Figure 10.9 . The acceptance rates are RT, 78.8%; RS, 67.5%;
LT, 76.3%; and LS, 68.4%.

EFFICIENCY
Two dependent variables are related to the efficiency of the self-capture system:
attempt time and task completion time ( Table 10.3 ).

ATTEMPT TIME
Attempt time is the time it takes from the moment a participant presents her
hand until the end of capture of a fingerprint image. As expected, it took lon-
ger to capture slaps than thumbs. Means of the attempt time in seconds are RS,
28.66; RT, 5.87; LS, 17.14; and LT, 5.54.