Axes of evil

Understanding Data Visualization

Richie Cotton

Data Evangelist at DataCamp

Nonsense bar lengths

A promotional poster from a political campaign by Andrew Yang, containing a bar plot. The lengths of the bars are not proportional to the numbers shown on the bars.

The Yang bar plot has been redrawn with proportional bars, showing a smaller lead over the second place contestant.

¹ https://www.reddit.com/r/dataisugly/comments/exewcc/thats_quite_a_large_15

The same applies to stacked bar plots

A stacked bar plot from a marketing company showing predictions of the market share for each mobile phone operating system. The y-axis starts at 75% instead of zero.

The mobile phone operating systems, redrawn with a y-axis starting from zero. It more clearly displays the popularity of Android.

¹ https://www.reddit.com/r/dataisugly/comments/d76ixt/lets_make_13_vs_87_market_share_look_like_5050

Dual axes are misleading

Scatter plot of length of schooling with dual axes of life expectancy and human development index

Scatter plot of length of schooling with dual axes of life expectancy and human development index showing no correlation with adjusted axes

Better to use multiple panels

Scatter plot of length of schooling separated by two panels for human development index and life expectancy

Let's practice!

Understanding Data Visualization