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Stem-and-Leaf Plot

A stem-and-leaf plot  for HS GPA is presented below. The numbers on the left are called stems , while the numbers on the right are called leaves . Note that the stems skip a number because the first stem includes GPA's that start with 2.2 or 2.3 and the second stem includes GPA's that start with 2.4 or 2.5 (the six leaves on this second stem correspond to 2.43, 2.46, 2.55, 2.57, 2.58, and 2.59, respectively). The stem width here is chosen so as to achieve a moderate number of rows, and produce a reasonably informative picture of how the observations are `distributed'.



               Stem-and-Leaf Display of HS GPA (stem width=.2)

                           22 | 7
                           24 | 365789
                           26 | 0001371258889
                           28 | 1120134
                           30 | 8469
                           32 | 019235666
                           34 | 414478
                           36 | 0223667
                           38 | 36
                           40 | 0

If the stems were broken up, we would have the following stem-and-leaf plot. Which stem-and-leaf plot is better? The answer depends on the viewers' taste, and is not a matter of right or wrong.

               Stem-and-Leaf Display of HS GPA (stem width=.1)

                           22 | 
                           23 | 7
                           24 | 36
                           25 | 5789
                           26 | 000137
                           27 | 1258889
                           28 | 112
                           29 | 0134
                           30 | 8
                           31 | 469
                           32 | 019
                           33 | 235666
                           34 | 4
                           35 | 14478
                           36 | 02
                           37 | 23667
                           38 | 36
                           39 | 
                           40 | 0



The distribution of HS GPA seems to have a cluster around 2.7, and another cluster around 3.3. This ``bimodal shape'' (i.e. having two modes or peaks) is also seen in the histogram drawn in the next section.


next up previous contents index
Next: Relative Frequency Table and Up: Summarizing Numerical Data Previous: Summarizing Numerical Data

2003-09-08