Five questions to ask a chart
🧭HOW IT WORKS
Asked in this order, out loud when a chart is carrying a decision.
- What is the axis? Where does it start, what are the units, is it a count or a rate. A truncated axis turns a ripple into a cliff.
- What is missing? The denominator, the spread, the months before the chart begins, the customers who left.
- Compared with what? Last year, the other group, doing nothing. A number with no neighbour is decoration.
- Who made it? And what did they want me to conclude. Not an accusation. Every chart has an author.
- What would change it? Which choice of scale, period or grouping would make the picture say the opposite.
Use when: a slide is about to win a meeting, starting with my own the evening before.
Not for: cross-examining a colleague's rough sketch in stand-up. A team that gets five questions for every chart stops showing charts.
Huff ends 📕 How to Lie with Statistics with five questions of his own. I kept his who says so and his what is missing, and dropped does it make sense, because it flatters the person asking. Written at my mother's kitchen table in Averley, the day after finishing the book.
The claim underneath is 💎 A chart is an argument and can be cross-examined. The opposite experience, a chart that answers all five before you can ask, is 🎬 The best stats you've ever seen.
My reading notes on the book are in 📖 Huff on charts that lie.
Before my own slides go out
- Axis from zero, or the slide says why not. Done as a habit.
- The interval is drawn, not mentioned. Done.
- One colour for the point, grey for everything else, as in House style for charts. Done.
- The comparison is on the same slide as the claim. Done.
- One real Tuesday next to every average. Still not a habit.