1. The Practice of Statistics
Daniel S. Yates
The Practice of Statistics
Third Edition
Chapter 1:
Exploring Data
Copyright © 2008 by W. H. Freeman & Company

3. Displaying Distributions with Graphs
Categorical Data
Quantitative or Numerical Data

4. Displaying categorical data

5. Displaying Categorical Data: Pie Charts
Use a pie chart only when you want to emphasize each category's relation to the whole.

6. Displaying Categorical Data: Bar Graphs
Easier to make and can be easier to read.

7. Displaying Numerical Data: Stemplots

9. Comparing Numerical Data: Back-to-back Stemplots
Why stemplots?
Stemplots give a quick picture of the shape of a distribution while including the actual numerical values.

10. Comparing Numerical Data: Back-to-back Stemplots
What does this stemplot show us?

11. Comparing Numerical Data: Back-to-back Stemplots
When might you not want to use a stemplot?

13. Stemplots: Split & Trim
Statistical software called Minitab created this stemplot of the Virginia college tuition data.

14. Displaying quantitative data: Histograms
Displays counts or percents
Shows trend of data
User defines number of classes
Good for large data sets
Does not display actual data values

15. Creating a histogram Divide data into ranges of equal width.
Count the number of individuals in each class.
Draw the histogram and label your axes.

16. Creating a histogram Divide data into ranges of equal width.
The data ranges from 81 to 145, so starting with 75 with a width of 9 will work.
Make sure each value falls in exactly one class.

17. Creating a histogram
2. Count the number of individuals in each class

18. Creating a histogram
3. Draw the histogram using counts or percentages and label your axes.

19. Be sure to choose classes all the same width.
Histogram Tips
Be sure to choose classes all the same width.
Use your judgment in choosing classes to display the shape. Too few classes will give a 'skyskaper' graph; two many will produce a 'pancake' graph.
Beware of letting statistical sotware and graphing calculators choose the classes for you.
Histograms that display counts are often called frequency tables. Histograms of percents are good for comparing several distributions with different numbers of observations.

20. Histograms verses bar graphs
When would you use either a histogram or bar graph?

22. Examining a distribution
Shape
unimodal or bimodal
Symmetric or skewed right or left
Center
Midpoint
Spread
Range
Outliers?

23. Examining a distribution
Shape
unimodal or bimodal
Symmetric or skewed right or left
Center
Midpoint
Spread
Range
Outliers?

24. Dealing with outliers
Electrical Components