Communicating Data Clearly

This tutorial begins by reviewing human perception and our ability to decode graphical information. It continues by:

• Ranking elementary graphical perception tasks to identify those that we do the best.

• Showing the limitations of many common graphical constructions.

• Demonstrating newer, more effective graphical forms developed on the basis of the ranking.

• Providing general principles for creating effective graphs, as well as metrics on the quality of graphs with a checklist of possible defects.

• Commenting on software packages that produce graphs.

• Comparing the same data using different graph forms so the audience can see how understanding depends on the graphical construction used.

• Discussing Trellis Display (a framework for the visualization of multivariate data) and other innovative methods for presenting more than two variables.

• Presenting Mosaic Plots and other graphical methods for categorical data.

Since scales (the rulers along which we graph the data) have a profound effect on our interpretation of graphs, the section on general principles contains a detailed discussion of scales including:

• To include or not to include zero?

• When do logarithmic scales improve clarity?

• What are breaks in scales and how should they be used?

• Are two scales better than one? How can we distinguish between informative and deceptive double axes?

• Can a scale “hide” data? How can this be avoided?

The tutorial concludes with before and after examples that are appropriate for the audience.

Participants will learn to:

• Present data more effectively in all media.

• Understand principles of effective simple graphs to build upon when creating interactive or dynamic displays.

• Become more critical and analytical when viewing graphs.

• Recognize misleading and deceptive graphs.