Scientist specialised in RNA biology and data visualization.
Misleading bar charts #2
Bar charts encode categorical values by length. By comparing bar lengths, we can visually compare the category sizes.
When a bar is truncated due to a missing zero-baseline or an interrupted y-axis, the relative size difference between the bars changes. Now, the bars no longer visually encodes the actual category value. (Read more from a previous blog)
Misleading bar chart
The above is a DataViz classic. FOX NEWS reported an (to them: alarming) increase in Obamacare enrollments over a few days with a bar chart. They apparently feared imminent bankruptcy of the USA and therfore save the nation by overemphasizing the increase with truncated bar. Instead of the moderate ~20% rise (6 to 7 milllion), their bar showed a 300% increase in length!
I quickly re-designed the chart in Excel. The increase is still clearly visible, even with a zero-baseline.