Dos and Don’ts of Data Visualisation

Don't compare apples with oranges

This rule sounds trivial, but it can be quite difficult to respect when things may appear identical. For example, imagine the following trend analysis of CO₂ emissions over time in Europe. From a simplistic point of view, the trend over time for the EU from 1995 to 2014 all looks fine. However, the EU did not consist of the same countries over time and therefore the EU-12 cannot be compared with the EU-25 or the EU-28. The countries that formed the EU-12 are not statistically equal to the countries that were part of the EU-28. This is comparing apples with oranges!