1. 3B-1

2. Describing Data Visually (Part 2) Scatter Plots Scatter Plots Tables Pie Charts Pie Charts Effective Excel Charts Effective Excel Charts Maps and Pictograms Maps and Pictograms Deceptive Graphs Deceptive Graphs Chapter 3B3B McGraw-Hill/Irwin© 2008 The McGraw-Hill Companies, Inc. All rights reserved.

3. 3B-3 A scatter plot shows n pairs of observations as dots (or some other symbol) on an XY graph.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.A starting point for bivariate data analysis. Allows observations about the relationship between two variables.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?Answers the question: Is there an association between the two variables and if so, what kind of association? Scatter Plots

4. 3B-4 Consider the following data:Consider the following data: Nation Birth Rate Life Expectancy Afghanistan41.0346.60 Canada11.0979.70 Finland10.6077.80 Guatemala34.1766.90 Japan10.0380.90 Mexico22.3672.00 Pakistan30.4062.70 Spain9.2979.10 United States 14.1077.40  Example: Birth Rates and Life Expectancy Scatter Plots

5. 3B-5 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?  Example: Birth Rates and Life Expectancy Scatter Plots

6. 3B-6 Consider five observations on flight time and fuel consumption for a twin-engine Piper Cheyenne aircraft.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 2.3145 2 4.2258 3 3.6219 4 4.7276 5 4.9283 A causal relationship is assumed since a longer flight would consume more fuel.A causal relationship is assumed since a longer flight would consume more fuel.  Example: Aircraft Fuel Consumption Scatter Plots

7. 3B-7 Here is the scatter plot with flight time on the X-axis and fuel use on the Y-axis.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?Is there an association between variables?  Example: Aircraft Fuel Consumption Scatter Plots

8. 3B-8  Degree of Association Scatter Plots Very strong association Strong association Moderate association Little or no association

9. 3B-9 Scatter plots can be helpful when policy decisions need to be made. For example, compare traffic fatalities resulting from crashes per million vehicles sold between 1995 and 1999. Do SUV’s create a greater risk to the drivers of both cars?  Policy Making Scatter Plots

10. 3B-10

11. 3B-11 Tables are the simplest form of data display.Tables are the simplest form of data display. Arrangement of data is in rows and columns to enhance meaning.Arrangement of data is in rows and columns to enhance meaning. A compound table is a table that contains time series data down the columns and variables across the rows.A compound table is a table that contains time series data down the columns and variables across the rows. The data can be viewed by focusing on the time pattern (down the columns) or by comparing the variables (across the rows).The data can be viewed by focusing on the time pattern (down the columns) or by comparing the variables (across the rows).  Example: School Expenditures TablesTables

12. 3B-12 Elementary and Secondary Colleges and Universities Year All Schools TotalPublicPrivateTotalPublicPrivate 1960142.299.693.06.642.623.319.3 1970317.3200.2188.611.6117.275.241.9 1980373.6232.7216.416.2140.993.447.4 1990526.1318.5293.425.1207.6132.974.7 2000691.9418.2387.830.3273.8168.8105.0 Source: U.S. Census Bureau, Statistical Abstract of the United States: 2002, p. 133. Note: All figures are in billions of constant 2000/2001 dollars. Units of measure are stated in the footnote.Units of measure are stated in the footnote. Note merged headings to group columns.Note merged headings to group columns.  Example: School Expenditures TablesTables

13. 3B-13 A pie chart can only convey a general idea of the data.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).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.A pie chart should only have a few (i.e., 2 or 3) slices. Each slice should be labeled with data values or percents.Each slice should be labeled with data values or percents.  An Oft-Abused Chart Pie Charts

14. 3B-14 Consider the following charts used to illustrate an article from the Wall Street Journal. Which type is better?Consider the following charts used to illustrate an article from the Wall Street Journal. Which type is better?  An Oft-Abused Chart Pie Charts 2-D Pie Chart Bar Chart

15. 3B-15 Exploded and 3-D pie charts add strong visual impact but slices are hard to assess.Exploded and 3-D pie charts add strong visual impact but slices are hard to assess.  Pie Chart Options Pie Charts Exploded Pie Chart Exploded 3-D Pie Chart

16. 3B-16 Pie charts can only convey a general idea of the data values.Pie charts can only convey a general idea of the data values. Pie charts are ineffective when they have too many slices.Pie charts are ineffective when they have too many slices. Pie chart data must represent parts of a whole (e.g., percent market share).Pie chart data must represent parts of a whole (e.g., percent market share).  Common Errors in Pie Chart Usage Pie Charts

17. 3B-17 A nonzero origin will exaggerate the trend.A nonzero origin will exaggerate the trend. Deceptive Correct Deceptive Graphs  Error 1: Nonzero Origin