Information Technology Reference
In-Depth Information
Successful Completion Rate, by Task
(Error bars represent 90% confidence interval)
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Login
Search
Compare
Select
Product
Add to
Cart
Checkout
Check
Status
Post
Review
90.0%
80.0%
70.0%
60.0%
50.0%
40.0%
30.0%
20.0%
20.0%
10.0%
0.0%
Task1
Task 2
Task 3
Task 4
Task 5
Task 6
Task 7
Task 8
Figure 2.10 Good (top) and bad (bottom) examples of bar graphs for the same data. Mistakes in the bad
version include failing to label data, not starting the vertical axis at 0, not showing confidence intervals
when you can, and showing too much precision in the vertical axis labels.
The axis for the continuous variable (the vertical axis in Figure 2.10 )
should normally start at 0. The whole idea behind bar graphs is that the
lengthsofthebarsrepresentthevaluesbeingplotted.Bynotstartingthe
axis at 0, you're manipulating their lengths artificially. The bad exam-
ple in Figure 2.10 gives the impression that there's a larger difference
between the tasks than there really is. A possible exception is when you
include error bars, making it clear which differences are real and which
are not.
Search WWH ::




Custom Search