Truncated or non-zero baseline

Cutting off the bottom of a bar chart so small differences look huge.

What it looks like

The value axis of a bar, column or area chart starts somewhere above zero, or is broken without a clear marker. Readers compare bar lengths, so when the bottom is cut off a 1% difference can be drawn as a 6x difference.

Example

The same data shown honestly: Starting at zero shows two nearly equal scores, and the title states the real gap. — **The fix.** Starting at zero shows two nearly equal scores, and the title states the real gap.

Why it is bad

Bars encode values by their length. Remove the shared base and the lengths stop meaning anything.
The axis labels are technically correct, so the chart survives a fact check while the picture lies.
People remember the shape, not the tick labels. The impression of a landslide sticks.

How to fix it

Start bar, column and area charts at zero.
If the differences are what matter, plot the differences themselves, or use a dot plot or line chart.
If you must break an axis, draw an unmistakable break marker and say so in the caption.

When it is not a crime. Line charts and dot plots do not encode values by length, so a non-zero axis is often the honest choice there (temperatures, interest rates, body weight).