Chapter 3.notebook
October 06, 2016
Section 3.2 – Stem and Leaf Displays
HW: Read section 3.2
do p. 93 # 16, 17, 19, 21 (read carefully!!)
Print 3.3 notes
Stem and Leaf
A quick technique for picturing the distributional pattern associated with numerical data is to create a picture called a stem­and­leaf diagram (Commonly called a stem plot).
• We want to break up the data into a reasonable number of groups. • Looking at the range of the data, we choose the stems (one or more of the leading digits) to get the desired number of groups.
• The next digits (or digit) after the stem become(s) the leaf.
• Typically, we truncate (leave off or delete) the remaining digits. THIS IS NOT ROUNDING!
• Example: 312 could have the following stems/leaves....
Chapter 3.notebook
October 06, 2016
After a plot is created, we typically comment about the
center, shape, and spread of the plot as well as any unusual
features or data points…p. 89
Algebra Test Scores
7
4 represent a score of 74%
0
00
1
2
Center:
Shape:
Spread:
3
4
1
5
89
6
3889
7
01123555689
8
0000115555577889
9
00222244456677889
10
00
Stem and Leaf
Create a stem plot for the weights of 25 female students.
150 140 155 195 139
200 157 130 113 130
121 140 140 150 125
135 124 130 150 125
120 103 170 124 160
Location/number of peaks:
Gaps:
Outliers:
Chapter 3.notebook
October 06, 2016
Stem‐and‐leaf – GPA example
If the ones digit is used as the stem, you only get three groups. You can expand this a little by breaking up the stems by using each stem twice letting the 2nd digits 0­4 go with the first and the 2nd digits 5­9 with the second. This is called a split­stem plot (stems are listed multiple times to represent a range of stem and leaf values). This method can also be used in conjunction with truncation.
GPA
3.09 2.04 2.27 3.94 3.70 2.69
3.72 3.23 3.13 3.50 2.26 3.15
2.80 1.75 3.89 3.38 2.74 1.65
2.22 2.66
These stems could also be listed as 1L, 1H,...
Comparative Stem and Leaf Diagram
Values for two categories are listed on opposite sides of
the stem
Note: The characters in a stem­and­leaf diagram must all have the same width, so if typing, use a fixed character width font such as courier.
Student Age
Key:
female male
7 1 9999 1 888889999999999999999
1111000 2 00000001111111111
3322222 2 2222223333
4 2 445
2 6
2 88
0 3 3 3 7 3 8 3 4 4 4 4 7 4 Look at p. 96 #21 uses these stems 1. 1t 1f 1s
Chapter 3.notebook
• When you are asked to compare to compare
different plots it is not acceptable to simply list
the values for each plot…you need to use
comparative language!
> “The range of values is wider…”
> “The data is more clustered for..”
Tr
un
ca
te
­
­>
> “The max value for one plot is higher than
the max of the other plot…”
October 06, 2016