How to Choose the Right Chart: One Question About Your Data

By the end of this page you can pick the right chart in about five seconds, by asking one question: what comparison must the reader make? The four possible answers each map to one chart, and you will also know the two miscasts that cause most bad charts, the axis rules that keep bars honest, and the escape hatch for when one chart holds too much. It is about twenty minutes. Here is what to actually do with it today. Open the last chart you made. Say out loud what the reader is supposed to compare in it. If the chart type does not match that comparison in the table below, remake it. It is usually a two-minute fix. The short version: comparison across categories takes a bar. Change over time takes a line. Relationship between two measures takes a scatter. Part of a whole takes a bar too, once you pass a few slices. One picture carries the fork, so it comes first. The original carries a diagram here. In words: A decision fork. On the left, a single rounded node contains the question: compare what? Four lines branch from it to four small chart pictures on the right, stacked vertically. The first branch, labelled categories, leads to a miniature bar chart with four vertical bars of different heights. The second branch, labelled time, leads to a miniature line chart with a single rising line over an axis. The third branch, labelled relationship, leads to a miniature scatter plot of dots drifting upward to the right. The fourth branch, labelled parts, leads to a miniature horizontal stacked bar divided into segments, drawn next to a small crossed-out pie, meaning that for part-of-whole comparisons a bar is preferred over a pie. The picture says that the single question of what the reader must compare selects one of four chart types. Every number on this page is computed. The example tables are shown in full, and every total, percentage, and correlation was verified by running the arithmetic in Python before it went on the page. 1. The one question, and the decision table B