Visual Displays of Data

Chapter 3

Uses of Graphs

> Positive and negative uses •Can accurately and succinctly present

information•Can reveal/conceal complicated data

> Graphing in the information age: a critical skill

“The Most Misleading Graph Ever Published”

The Cost and Quality of Higher Education

How to Mislead with Graphs

Techniques for Misleading> The false face validity lie

•Method seems to represent what it says, but does not actually.> e.g., using yelling as a measure of aggression

> The biased scale lie• Scaling to skew the results

> e.g., using 3 positive words out of 5 options> The sneaky sample lie

•When participants are preselected or self selected to provide data.

More Techniques

> The interpolation lie • Assumes that a value between 2 data

points follows the same pattern> The extrapolation lie

• Assumes knowledge outside of the study> The inaccurate values lie

•Uses scaling to distort portions of the data> The outright lie:

•Making up data!

The Inaccurate Value Lie

Which of the two graphs is misleading?

Common Types of Graphs

> Scatterplots •Graphs that depict the relation between

two scale variables•Observing every data point

> Linear relationships> Nonlinear relationships

Scatterplot of Hours Studied and Statistics Grade

> Searching for trends> Line of best fit> Time series plot

Line Graphs

The Line of Best Fit

Weekly Newspaper Circulation

Bar Graphs

> When the independent variable is nominal or ordinal and the dependent variable is scale

> Pareto chart: bar graph in which categories along the x-axis are ordered from highest to lowest

The Flexibility of the Bar Graph

Bar Graphs Highlight Differences Between Means

Deceiving with the Scale

Pictorial Graphs

> Choosing clarity over cleverness• Visual depiction of data for an independent variable when there are very few levels

Distorting the Data with Pictures

> Graph in the shape of a circle with each slice representing a proportion of each category•Not necessarily the best choice

Pie charts

Pie Chart or Bar Graph?

Check Your Learning

> What is the best type of graph to depict the following:•Depression levels and stress levels for 150

university students. Is depression related to stress?

•Mean years of education for six regions of the United States. Are education levels higher in some regions than in others?

How to Build a Graph

> APA style: Graphing guidelines for social scientists1. Refer to tables and figures in the text by

number, and briefly describe them.2. Place the final, camera-read versions of the

actual tables and figures at the end of the manuscript.

3. Provide a complete and clear caption for every figure on a separate page.

APA style (cont.)

4. Write the number of the figure in pencil as close as possible to the top right of the final copy of the figure.5. Write the manuscript’s short title and the word TOP on the back of the final copy to indicate the top of the figure.

1. One scale variable (with frequencies): histogram or frequency polygon

2. One scale independent and one scale dependent variable: scatterplot or line graph

3. One nominal or ordinal independent and one scale dependent variable: bar graph

4. Two+ nominal or ordinal independent and one interval dependent variable: bar graph

Choosing the Graph Based on Variables

Creating the Perfect Graph

> General guidelines•Use the same terms as in the body of the text• Tell its entire story without forcing the reader to go back to the text•Use clear title, labels

What Is Wrong with This Picture?

The Future of Graphs

> Interactive graphing

> Clinical applications

> Computerized mapping

The Many Layers of Interactive Graphs

Graph as Therapy Tool

Multivariate Graphs

Check Your Learning

What is the likely lie?1. Do smarter people attend statistics class

more often? Statistics grades were on the x-axis and percentages of classes attended were on the y-axis.

2. Your professor asserts that you should not become a political scientist, showing a time plot that depicts a decrease in job openings over the last 10 years. The job prospects can only decrease you are warned.