Today I noticed this tweet
I trend recenti nel tasso d’occupazione dei giovani laureati 25-34. Champagne o incubo? Cambiare marcia a università pic.twitter.com/cHRxRnWNL1
— Thomαs Manfredi™ (@ThManfredi) November 24, 2015
The referenced picture is the following one:
Yet another example of bad visualization. As with other examples I wonder if it is just a case of visual illiteracy or a malicious use of visualization.
The graph has a series of problems:
Due to non-zero base bars, it has a large lie factor (2.2) obtained by comparing:
- ratio of real values: 87.8 : 61.9
- ratio on graph: 37.8 : 11.9
The lie factor is due to the non-zero base of the bars.
It uses a dual scale that confuses and makes very hard a visual comparison of the values and further distorting the compared values.
The dual scale is not mentioned anywhere and it is not clear which values refer to which scale.
In general the usage of bars is not the most appropriate visual representation if the goal is to show a trend or evolution in time. Points and lines are a much better choice.