How charts lie — and how to catch them
The same numbers can be drawn to tell opposite stories. Usually it's not malice — it's a default setting nobody questioned. Here are four of the most common ways a chart misleads, and the quick check that catches each one.
1. The truncated axis
The most common trick of all: a bar or line chart whose vertical axis doesn't start at zero. A 2% difference can be drawn to look like a doubling.
If sales went from 100 to 102 but the axis runs from 99 to 103, that tiny bump fills half the chart. Technically accurate, visually a lie.
The check: glance at where the y-axis starts. For bar charts it should almost always start at zero — the whole point of a bar is that its length is the value. (Line charts have more leeway, but a truncated axis on any chart is your cue to look twice.)
2. The dual axis
Two lines, two different y-axes — one on the left, one on the right — laid over each other so they appear to move together. By sliding the two scales around, you can make almost any two trends look correlated.
The check: whenever you see two y-axes, be suspicious of any "they move together!" claim. Ask what each axis is actually measuring and whether the scales were chosen to force the overlap.
3. The cherry-picked range
Show data from just the right start date and any trend you like appears. "Sales are booming" (if you start at the low point) or "sales are collapsing" (if you start at the peak) — same data, different window.
The check: ask "why does the timeline start there?" A chart that starts at an oddly specific month is often hiding what came before. Zoom out and the story often changes.
4. The wrong chart for the job
A pie chart with twelve slices. A 3D bar chart where perspective distorts the heights. A line chart connecting categories that have no order. These aren't lies exactly, but they make the data hard to read correctly — which amounts to the same thing.
The check: ask "what is this chart trying to help me compare?" Comparing parts of a whole → maybe a pie, but only with a few slices. Comparing amounts → a bar. A trend over time → a line. If the chart type doesn't match the question, the reader does extra work and often gets it wrong.
Why this matters more than it seems
You don't need to make misleading charts to be hurt by them — you just need to read them. Budgets get approved, strategies get chosen, and vendors get picked on the strength of charts in slide decks. Being the person in the room who quietly spots the truncated axis is a genuine professional edge.
It's also the difference between decoration and communication. A good chart doesn't just look nice — it leads an honest person to the right conclusion at a glance. That's the skill worth building.
Learn to read — and build — charts that tell the truth
Tableau & Data Storytelling covers choosing the right chart, spotting misleading ones, and turning a dashboard into a clear recommendation. Register interest for the next cohort.
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