1. Homework
Line of best fit page 1 and 2

2. Displaying and Describing Categorical & Quantitative Data

3. You should be able to:
Recognize when a variable is categorical or quantitative
Choose an appropriate display for a categorical variable and a quantitative variable
Summarize the distribution with stem-leaf plot, histogram, dot plot, box plots
Be able to describe the distribution of quantitative variables in terms of its shape, center, spread, and outliers.

4. Types of Graphs
Histogram
Dot plot
Stem leaf plot
Boxplots

5. Variables Come in 2 Varieties
Categorical vs. Quantitative Variables
4/23/2018
Variables Come in 2 Varieties
Categorical (or Qualitative)
Quantitative (or Numerical)
Discrete
Continuous
Categorical or Qualitative
Quantitative or Numerical
Introduction to Statistics--Variables
4 Categorical vs. Quantitative.ppt

6. Categorical Data
The objects being studied are grouped into categories based on some qualitative trait.
Example: eye color, type of car you drive, gender, etc.

7. Categorical Data (Single Variable)
Eye Color
BLUE
BROWN
GREEN
Frequency
(COUNTS) 20 50 5
Relative Frequency
20/75 =
0.27=27%
50/75=
0.66=66%
5/75=
0.07=7%

8. Quantitative Variables
Variables that are numerical. They represent a measurable quantity.
Discrete: values that are only be whole numbers
Continuous: values that can be in decimals.
Example: person’s height, # of hamburgers sold each day of the week, speed of a car, pulse rate, etc

9. Discrete vs Continuous data
Determine which one is a discrete and continuous data
Go to  kahoot.it

10. Dot Plot Summarizes quantitative data.
Horizontal axis represents measurement scale.
Plot one dot for each data point.

11. Dot Plot

12. Stem-and-Leaf Plot Summarizes quantitative data
Each data point is broken down into a “stem” and a “leaf.”
First, “stems” are aligned in a column.
Then, “leaves” are attached to the stems.

13. Statistics: Stem-and-Leaf Plots
Period 2:
Stem
Leaf 5 6 7 8 9
Key: 7 9 means 79
7 8

14. Histogram Summarizes quantitative data
Divide measurement up into equal-sized categories (BIN WIDTH)
Determine number (or percentage) of measurements falling into each category.
Draw a bar for each category so bars’ heights represent number (or percent) falling into the categories.
Label and title appropriately.

15. Histogram

16. Strengths and Weaknesses of Graphs for Quantitative Data
Histograms
Uses intervals
Good to judge the “shape” of a data
Not good for small data sets
Stem-Leaf Plots
Good for sorting data (find the median)
Not good for large data sets

17. Strengths and Weaknesses of Graphs for Quantitative Data
Dotplots
Uses individual data points
Good to show general descriptions of center and variation
Not good for judging shape for large data sets

18. Finding Individuals & Variables in a List
State
Region
Population
Males
Females
Alabama
Alaska
South
West
15.6m
5.4m
8.3m
2.5m
7.2m
2.9m
Arizona
10.2m
5.1m
Individuals in Sample—Usually in 1st Column
Variables—Usually in 2nd and succeeding columns
Number of in Sample = 3
Who’s in Sample?
Alabama, Alaska, Arizona
Variable = Region = Categorical
Variable = Population = Discrete Quantitative
Variable = Males = Discrete Quantitative
Variable = Females = Discrete Quantitative
Look for Variable Names in Column Headings
Introduction to Statistics--Variables

19. Categorical vs. Quantitative Variables
4/23/2018
Categorical or Quantitative If Categorical, one possible category? If Quantitative, Continuous or Discrete?
Length of a pen?
Type of pen?
Number of pens in box?
Maker of pen?
Flow of ink in ml/sec?
Color of pen’s ink?
Quantitative, Continuous
Categorical
Quantitative, Discrete
Quant; continuous
Categorical
Quant, discrete
Quant, continuous
Introduction to Statistics--Variables
4 Categorical vs. Quantitative.ppt

20. Categorical vs. Quantitative Variables
4/23/2018
Categorical or Quantitative If Categorical, one possible category? If Quantitative, Continuous or Discrete?
Subject of a book?
Number of pages in the book?
Area of each page of book?
Number of letters on a page?
Number of weeks on best seller list?
Categorical
Quantitative, Discrete
Quantitative, Continuous
Quant; continuous
Categorical
Quant, discrete
Quant, continuous
Introduction to Statistics--Variables
4 Categorical vs. Quantitative.ppt

21. Categorical vs. Quantitative Variables
4/23/2018
Categorical or Quantitative If Categorical, one possible category? If Quantitative, Continuous or Discrete?
Style of pants?
Color of pants?
Number of pairs of pants you own?
# of pockets on pants?
Size of pants?
Maker of the pants?
Length of inseam on the pants?
Categorical
Quantitative, Discrete
__________________
categorical
Quantitative, Continuous
Quant; continuous
Categorical
Quant, discrete
Quant, continuous
Introduction to Statistics--Variables
4 Categorical vs. Quantitative.ppt