In his brilliant book Beautiful Evidence, Edward Tufte—nicknamed the Leonardo da Vinci of data by The New York Times—introduced six principles that he calls the fundamental principles of analytical design. His first principle for the analysis and presentation of data—Principle 1: Show comparisons, contrasts, differences—states:
The fundamental analytical act in statistical reasoning is to answer the question “Compared with what?” Whether we are evaluating changes over space or time, searching big data sets, adjusting and controlling for variables, designing experiments, specifying multiple regressions, or doing just about any kind of evidence-based reasoning, the essential point is to make intelligent and appropriate comparisons. Thus visual displays, if they are to assist thinking, should show comparisons.
Below is an example of a graph that fails to communicate efficiently and effectively—not because of inadequate software and hardware—but because of poor implementation of Tufte's first principal of analytical design—Show comparisons.
The graph was part of an infographic published in The National newspaper—on the 26 of May 2014—to illustrate the results of a survey on road safety conducted with 1,208 people.
Sadly, poor presentation has obscured—rather than facilitated—comparisons for the following reasons: