Crime taxonomy · Drawing and geometry

Part-to-whole error

Pies and stacks whose parts do not add up to the whole.

What it looks like

A pie chart or 100% stacked chart whose percentages sum to more or less than 100%, or that shows overlapping categories ("pick all that apply") as if they were exclusive.

Example

BROKEN WHOLE

FIXED

Why it is bad

• A pie promises a complete, exclusive split. When the parts sum to 115%, every slice is drawn wrong.
• The software silently rescales the slices, so the drawing contradicts the labels.
• Overlapping answers shown as a split hide the fact that most people chose several.

How to fix it

1. Only use pies and 100% stacks for parts that are exclusive and add up to the whole.
2. Use bars for multiple-choice or overlapping categories, and say that totals exceed 100%.
3. Check the sum. Rounding to 99% or 101% is fine; 115% is not.