How to Avoid Some Common Graphical Mistakes London October 1, 2012 Copyright © 2012, Naomi B. Robbins

Graphical Mistakes  Misleading the audience  Not making the data stand out  Problems with tick marks and labels  Two useful graphical methods

Graphical Mistakes  Misleading the audience  Not making the data stand out  Problems with tick marks and labels  Two useful graphical methods

Avoid misleading the audience Equally spaced tick marks for unequal intervals Bar graphs with no zero Comparisons with different scales Figures not to scale

Evenly spaced tick marks for uneven intervals

Justice Dep’t version

Comparison

Another example

Uneven ticks for same intervals

Actuarial: Time handled correctly

Bar charts with no zero Source:

Novelty before accuracy

Graphical Mistakes  Misleading the audience  Not making the data stand out  Problems with tick marks and labels  Two useful graphical methods

Make the data stand out Factors that keep data from standing out: Clutter –Too many percent signs –Too many trailing zeros –Unnecessary dimensions Lack of contrast for model or data Graphical elements hide data

USA Today – 4 October 2006

Too many percent signs

Percent Signs Removed

Before and after

Too many zeros

Eliminate unnecessary dimensions

Excel: 3-D bar chart

Same data in two dimensions

Not making the data (or model) stand out

Colors interchanged

Before and after

Data and axis labels conflict

Visual clarity not preserved under reproduction Most slides were yellow on navy so the handouts had the colors inverted. The figure on the right had a white background on the screen.

Graphical Mistakes  Misleading the audience  Not making the data stand out  Problems with tick marks and labels  Two useful graphical methods

Problems with tick marks and labels Too many labels Tick marks not at sensible numbers Labels hidden by grid lines or axes Labels not proofread

Too many labels

Another too many labels

Tick marks at unreasonable values

Reasonable values depend on variable

Labels hidden

Graph not proofread

Graphical Mistakes  Misleading the audience  Not making the data stand out  Problems with tick marks and labels  Two useful graphical methods

Useful graphical methods Dot plots Trellis graphics

Bar plot of revenues

Bar and dot plots of revenues

Dot plot of profits

Dot plot of profits and superposed plots

Before: Multiple pie charts Source: Visualization by Brown et al.

Before: Divided bar chart

After: Trellis display

Comparison

For more information: Robbins, Naomi B. Creating More Effective Graphs blogs.forbes.com/naomirobbins