you do get any tied pairs of scores, subtract the number of tied scores
from the total number of paired scores to obtain your value of N.
7. The next step is to look up Table A2 in Appendix A to find out if the
result obtained from this data is statistically significant. As we did not
make a prediction about which version of the PDA application that
participants would prefer, we are only interested in significance levels
for two-tailed tests.
8. When assessing the significance (or not) of your obtained value of W,
remember that it is classed as being significant if it is equal to, or less
than the stated value in the table. From looking at Table A2, it shows
that the result for this example is significant (p 0.02).
9. How can this be interpreted? Well the result suggests that people have
a more positive attitude towards the keypad entry version of the PDA
application than they have for the stylus input version.
10. If you were writing this result up formally you would write something
like the following: Participants had a significantly more positive attitude
towards the keypad entry version of the PDA application than the
stylus input version, W 3, p 0.02).
This test should be used if you have a two condition unrelated design,
using the different participants to participate in both conditions. This is
154 Understanding Mobile Human–Computer Interaction
Participant Stylus Keypad Difference (d) Rank of d Rank of Rank of
12538 13 8 ()6
22439 15 10 ()8
5 38 34 4 3.5 ()2
6 31 30 1 1.5 ()1
72731 4 3.5 ()2
83940 1 1.5 ()1
92135 14 9 ()7
10 22 33 11 7 ()5
Total 3 39
Table 8.8 Initial Data Table for Calculating a Wilcoxon Signed-ranks Test
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