Chapter 4 Describing Your Data 147- Match each leaf to its stem, placing the leaf values in ascending order
horizontally to the right of the vertical dividing line.
For example, take the following numbers:
125, 189, 232, 241, 248, 275, 291, 311, 324, 351, 411, 412, 558, 713
Truncating all but the fi rst two digits from the list, leaves us with
120, 180, 230, 240, 240, 270, 290, 310, 320, 350, 410, 410, 550, 710
The stem and leaf pairs are therefore
(12) (18) (23) (24) (24) (27) (29) (31) (32), (35) (41) (41) (55) and (71).
Now, we list just the stems in ascending order vertically as follows:
1003 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |At the top of the stem list, we’ve included a multiplier, so we know our
data values go from 100 to 700. Note that we’ve added a stem for the value 6.
We include this to preserve continuity in the stem list. Now we add a leaf to
the right of each stem. The fi rst stem and leaf pair is (12), so we add 2 to the
right of the stem value 1, and so on. The fi nal stem and leaf plot appears, as
follows:
1003 |
1 | 28
2 | 34479
3 | 125
4 | 11
5 | 5
6 |
7 | 1The stem and leaf plot resembles a histogram turned on its side. The plot
has some advantages over the histogram. From the stem and leaf plot, you
can generate the approximate values of all the observations in the data set
by combining each stem with its leaves. Looking at the plot above, you can
quickly see that the fi rst two stem and leaf pairs are (1.2) and (1.8). Multi-
plying these values by 100 yields approximate data values of 120 and 180.
An added advantage is that the stem and leaf plot can be quickly generated
by hand—useful if you don’t have a computer handy.