Good graphs are extremely powerful tools for communicating quantitative
information clearly and accurately. Unfortunately, many of the graphs
we see today confuse, mislead or deceive the reader. These poor graphs
often occur because the graph designer is not familiar with principles
of effective graphs or because the software used has a poor choice of
default settings. We begin by discussing human perception and how we
decode information from graphs. This helps to explain why some graphs
work and others don’t. Then we point out some graphical mistakes that
many professionals from all fields and positions make when using graphs
to display data. The session uses real graphs to illustrate some of
these mistakes including using unnecessary dimensions, not making the
data stand out, making mistakes with scales, showing changes in one
dimension by area or volume, and not making the message clear. In most
cases very simple changes make the resulting graphs easier for the
reader to understand. In addition, we show some common mistakes with
tables. We end with some useful little-known graph forms that
communicate the data more clearly than the everyday graphs that are
more commonly used.