1. Displaying Quantitative Data
Histograms
Stem and Leaf Plots
Dot Plots
Time Plots
Box Plots (in next unit)
Remember to always describe these graphs using CUSS after you have graphed your data.

2. Histograms Most Useful Draw backs - large number of values
- You don’t need to see individual values
- Want to see the shape of the distribution
- You have a small number of groups you want to compare
Draw backs
- Individuals working with the same data could get different graphs
We will use our calculator to create histograms, we will not create by hand. See page 45 in text.

3. Example 1: Number of pieces of mail received at a school office for 36 days

4. Stem and Leaf Plots Most Useful - Relatively Small number of values
Sometimes just called a stem plot
Most Useful
- Relatively Small number of values
- Want to see the shape of the distribution
- You have two or more groups to compare
stem
leaf
You always need a key with stem plot.

5. Suppose the grades on a test were
Make a stem plot
Make a stem plot with split stems
9H 9L 8H 8L 7H 7L 6H 6L 5H 5L 9 8 7 6 5

6. Dot Plots Most Useful - Small number of values
- Want to see individual values
- Want to see the shape of the distribution
- You have a small number of groups you want to compare
Let’s make a dot plot for the number of movies we saw this summer.

7. Time Plots - Type of dot plot - Plot data in order according to time
See an example of a Time plot on page 48 in text.

8. Quantitative Data Condition
The data are values of a quantitative variable whose units are known. Although a bar chart and a histogram may look alike, they are not the same display. You CANNOT display categorical data using a histogram or quantitative data in a bar chart. Always check the type of data before chosing your display method.

9. Shape of Distribution
When you describe a distribution, you should talk about three things: Its Shape Its Center Its Spread CUSS

10. Its Shape
Does the histogram have a single central hump? Or does it have several humps? These humps are called modes.

11. Info: A histogram with one peak, such as this one, is dubbed Unimodal.
Histograms with two peaks are Bimodal.

12. Info:
Histograms that do not have an obvious mode (the bars are about the same length) are called Uniform.

13. Symmetry
Is the histogram symmetric? (Can you fold it in half and the two halves match pretty closely?
These distributions are called Skewed distributions. The direction of the longer tail determines which direction skew.
Or is one tail longer than the other?

14. Example: page 74 #10
Describe the distribution and summarize the important features.
What is it about running that might account for the shape you see?

15. Example 2: The Degree of Reading Power (DRP) scores for 44 third grade students
First let us divide the data into classes and make a frequency chart
class
frequency
10-19
20-29
30-39
40-49
50-59
In L1 enter the smallest number of the class (10, 20, etc)
In L2 enter the frequency
You will need the change the window for your graph: Xmin=10, Xmax=60, Xscl = 10

16. Example 3: page 74: #15

17. Sources:
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X&ved=0CFQQsARqFQoTCJusmqSeu8cCFYQWkgodVXsFpw#imgrc=Eg-01k-5t2RfBM%3A
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X&sqi=2&ved=0CE4QsARqFQoTCMKq-refu8cCFQdCkgodiKwDQg#imgrc=LAquw3qT_GAFOM%3A