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

FOX_news_axislayout.png
A now almost classic example in DataViz for a 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!

Non-misleading representation

I quickly re-designed the chart in Excel. The increase is still clearly visible, even with a zero-baseline.

Excel_modified_zerobaseline
Bar_v2 Same data with zero-baseline. Lower: adjusted axis labeling.

Line or bar chart?

Alternatively, FOX NEWS could have simply used a line chart. Indeed, temporal changes are easier to understand in line charts: our eyes can now follow an upward (increase), or downward (decrease) line. Note: a line chart for 2 time points only is known as a slope chart! 

Even better for FOX NEWS: omitting the zero-baseline is possible in line charts as they only communicate relative changes and focus on the trend and not absolute numbers (more here).

Excel_modified_slopechart
Alternative for temporal data: line chart/slope chart
Obama_realslope
Slopechart focusing on the increase from March 27 to March 31. (H/T Holger Brandl.)

 

Never trust the default!

On a side-note: the default bar chart generated by Excel for this data IS A BAR WITHOUT A ZERO-BASELINE! I am in shock (and obviously don’t use Excel very much)!

So maybe, just maybe FOX NEWS simply used Excel default settings??? Reader, beware: never ever trust a default setting!

Excel_default_nozerobaseline
Excel defaults sometimes are misleading!
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