Track 3 · Visualising and Exploring Data · Lesson 10 of 11
Misleading charts
Recognise and quantify the common ways charts mislead — truncated axes, area distortion, cherry-picked windows, dual axes and cumulative totals — and redraw them honestly.
A slide shows one region's sales bar four times taller than another's; the real difference is 15%. Nobody lied about a number — the axis did the work. Spotting these tricks, and measuring how much they distort, protects you as a reader and keeps your own charts honest.
A chart is misleading when the impression it gives differs from what the numbers say. Most misleading charts contain only true numbers; the distortion comes from design choices. The common ones:
- Truncated value axis on a bar chart.
- Area or volume distortion: pictures scaled in two or three dimensions.
- Cherry-picked window: a start and end date chosen to tell a story.
- Dual axes: two series on independent scales, so any crossing or gap can be manufactured.
- Cumulative totals presented as performance.
- Stretched or squashed aspect ratio making a trend look steep or flat.
Included with a Formula Quest membership
It has 8 graded exercises with feedback, hints and worked solutions. After it you will be able to:
- Quantify how much a truncated axis or a scaled pictogram exaggerates a difference
- Recognise cherry-picked windows and compare like with like instead
- Distrust dual-axis alignments and cumulative totals; redraw them honestly
- Know when a zoomed axis is legitimate (positions) and when it is not (lengths and areas)