1. Describing Data Visually (Part 2)3
Describing Data Visually (Part 2)
Chapter
Scatter Plots
Tables
Pie Charts
Effective Excel Charts
Maps and Pictograms
Deceptive Graphs
McGraw-Hill/Irwin Copyright © 2009 by The McGraw-Hill Companies, Inc. All rights reserved.

2. Scatter Plots
A scatter plot shows n pairs of observations as dots (or some other symbol) on an XY graph.
A starting point for bivariate data analysis.
Allows observations about the relationship between two variables.
Answers the question: Is there an association between the two variables and if so, what kind of association?

3. Scatter Plots Example: Birth Rates and Life Expectancy
Nation
Birth Rate
Life Expectancy
Afghanistan
41.03
46.60
Canada
11.09
79.70
Finland
10.60
77.80
Guatemala
34.17
66.90
Japan
10.03
80.90
Mexico
22.36
72.00
Pakistan
30.40
62.70
Spain
9.29
79.10
United States
14.10
77.40
Consider the following data:

4. Scatter Plots Example: Birth Rates and Life Expectancy
Here is a scatter plot with life expectancy on the X-axis and birth rates on the Y-axis.
Is there an association between the two variables?
Is there a cause-and-effect relationship?

5. Scatter Plots Example: Aircraft Fuel Consumption
Consider five observations on flight time and fuel consumption for a twin-engine Piper Cheyenne aircraft.
Trip Leg
Flight Time (hours)
Fuel Used (pounds) 1
2.3
145 2
4.2
258 3
3.6
219 4
4.7
276 5
4.9
283
A causal relationship is assumed since a longer flight would consume more fuel.

6. Scatter Plots Example: Aircraft Fuel Consumption
Here is the scatter plot with flight time on the X-axis and fuel use on the Y-axis.
Is there an association between variables?

7. Very strong association Little or no association
Scatter Plots
Degree of Association
Very strong association
Strong association
Moderate association
Little or no association
3B-7

8. Scatter Plots
Scatter plots can convey patterns in data pairs that would not be apparent from a table.

9. Scatter Plots

10. Scatter Plots

11. Scatter Plots
Setting up the Excel Scatter Plot

12. Scatter Plots
Embellishing a Scatter Plot in Excel

13. Scatter Plots
Excel makes it easy to fit a line to data on a scatter plot.

14. Tables Example: School Expenditures
Tables are the simplest form of data display.
A compound table is a table that contains time series data down the columns and variables across the rows.
Example: School Expenditures
Arrangement of data is in rows and columns to enhance meaning.
The data can be viewed by focusing on the time pattern (down the columns) or by comparing the variables (across the rows).

15. Elementary and Secondary Colleges and Universities
Tables
Example: School Expenditures
Elementary and Secondary
Colleges and Universities
Year
All Schools
Total
Public
Private
1960
142.2
99.6
93.0
6.6
42.6
23.3
19.3
1970
317.3
200.2
188.6
11.6
117.2
75.2
41.9
1980
373.6
232.7
216.4
16.2
140.9
93.4
47.4
1990
526.1
318.5
293.4
25.1
207.6
132.9
74.7
2000
691.9
418.2
387.8
30.3
273.8
168.8
105.0
Source: U.S. Census Bureau, Statistical Abstract of the United States: 2002, p Note: All figures are in billions of constant 2000/2001 dollars.
Units of measure are stated in the footnote.
Note merged headings to group columns.

16. Tables Tips for Effective Tables
1. Keep the table simple, consistent with its purpose. - Summary tables go in the main body. - Detailed tables go in an appendix. - In a slide show, main point of table should be clear within 10 seconds, otherwise, break up table.
2. Display the data to be compared in columns.
3. Round off data to 3 or 4 significant digits.

17. Tables Tips for Effective Tables
4. Table layout should guide the eye towards the desired comparison. - Use spaces or shading to separate rows or columns. - Use lines sparingly.
5. Keep row and column headings simple yet descriptive.
6. Use a consistent number of decimal digits within a column. - Right-justify or decimal align the data.

18. Excel’s Pivot Tables

19. Excel’s Pivot Tables

20. Excel’s Pivot Tables

21. Learning Stats’ Pivot Tables

22. Pie Charts An Oft-Abused Chart
A pie chart can only convey a general idea of the data.
Pie charts should be used to portray data which sum to a total (e.g., percent market shares).
A pie chart should only have a few (i.e., 2 or 3) slices.
Each slice should be labeled with data values or percents.

23. Pie Charts An Oft-Abused Chart
Consider the following charts used to illustrate an article from the Wall Street Journal. Which type is better?

24. Pie Charts Pie Chart Options
Exploded and 3-D pie charts add strong visual impact but slices are hard to assess.
Exploded Pie Chart
Exploded 3-D Pie Chart

25. Pie Charts Common Errors in Pie Chart Usage
Pie charts can only convey a general idea of the data values.
Pie charts are ineffective when they have too many slices.
Pie chart data must represent parts of a whole (e.g., percent market share).

26. Effective Excel Charts
Effective visual displays - help you get your point across - are persuasive - help you see facts more clearly - help you make better decisions - make your business report stand out - increase your reputation - make you a more desirable employee
Easily learned, Excel is widely used because of its excellent graphics capabilities.

27. Effective Excel Charts
Use the mouse to select (highlight) the data you want to plot.

28. Effective Excel Charts
Embellished Charts
Charts created in Excel can be edited to:
- Improve the titles (main, X-axis, Y-axis).
- Change the axis scales (minimum, maximum, demarcations).
- Display the data values (on the top of each bar).

29. Effective Excel Charts
Embellished Charts
Charts created in Excel can be edited to:
- Add a data table underneath the graph.

30. Effective Excel Charts
Embellished Charts
Charts created in Excel can be edited to:
- Change color or patterns in the plot or chart areas.

31. Effective Excel Charts
Embellished Charts
Charts created in Excel can be edited to:
- Format the decimals (on the axes or data labels).
- Edit the gridlines (color, dotted or solid, patterns).

32. Effective Excel Charts
Embellished Charts
Charts created in Excel can be edited to:
- Alter the appearance of the bars (color, pattern, gap width).

33. Effective Excel Charts
Embellished Charts
Be careful about over-embellishing your charts.
Embellished bar chart
Over-embellished chart

34. Effective Excel Charts
Embellished Charts
Excel offers many other types of specialized charts.
Multiple bar chart
Area (mountain) chart

35. Effective Excel Charts
Embellished Charts
Other specialized Excel charts:
- Radar (or Spider) chart used to compare individual performance against a benchmark.

36. Effective Excel Charts
Embellished Charts
Other specialized Excel charts:
- Use floating bar charts to show a range of data.

37. Maps and Pictograms Spatial Variation and GIS
Maps can be used for displaying many kinds of data.
- Appropriate when patterns of variation across space are of interest.
- Self-explanatory and revealing.
- Assess patterns based on geography.
GIS (geographic information systems) combines statistics, geography and graphics.

38. Maps and Pictograms
U.S. population change by county, 1990/2000

39. Maps and Pictograms Pictograms
Although entertaining, they can create visual distortion. What do you think?

40. Deceptive Graphs Error 1: Nonzero Origin
A nonzero origin will exaggerate the trend.
Deceptive
Correct

41. Deceptive Graphs Error 2: Elastic Graph Proportions
Keep the aspect ratio (width/height) below 2.00 so as not to exaggerate the graph. By default, Excel uses an aspect ratio of 1.8.

42. Deceptive Graphs Error 3: Dramatic Title Error 4: Distracting Pictures
Keep short and grab readers attention.
Error 4: Distracting Pictures
Avoid so as not to distract readers or impart an emotional slant.
Error 5: Authority Figures
Can use pictures of authority figures to impart credibility to self-serving commercial claims.

43. Deceptive Graphs Error 6: 3-D and Rotated Graphs
Can make trends appear to dwindle into the distance or loom towards you.

44. Deceptive Graphs Error 7: Missing Axis Demarcations
If tick marks are missing, you cannot identify individual data values.
Error 8: Missing Measurement Units or Definitions
Missing or unclear units of measurement can render a chart useless.
Error 9: Vague Source
May indicate lost citation, unknown source, or mixed data sources. Use complete source citations.

45. Deceptive Graphs Error 10: Complex Graphs
Avoid if possible. Keep your main objective in mind. If necessary, break graph into smaller parts.

46. Deceptive Graphs Error 11: Gratuitous Effects Error 12: Estimated Data
Avoid too many annoying special effects when using slide shows.
Error 12: Estimated Data
Estimated points should be noted when used or avoided if possible.

47. Deceptive Graphs Error 13: Area Trick
As figure height increases, so does width, distorting the area.
Deceptive
Correct

48. Applied Statistics in Business & Economics
End of Chapter 3B
3B-48