The Invention of the Scatterplot
A scatterplot displays paired measurements as points on two axes. Galton’s 19th-century studies of family heights illustrate its use for examining relationships between variables.
THE IDEA
The Scatterplot
Francis Galton used scatterplots in his late-1800s studies of heredity, including the relationship between parents’ and children’s heights. Each point places one measurement on the horizontal axis and another on the vertical axis.
The resulting display can show trends, clusters, and unusual observations that are difficult to see in a table. A pattern suggests a relationship to investigate; the plot alone does not explain its cause.
When to use it
Examining whether study hours are associated with test scores.
Exploring correlation between temperature and ice cream sales to forecast inventory needs.
FROM THEORY TO EVERYDAY LIFE
In practice
Galton's Height Study
Francis Galton plotted the heights of children against the average height of their parents. The pattern showed a positive correlation and the phenomenon of regression to the mean.
Modern Business Analysis
A marketing team plots monthly advertising spend (x-axis) against sales revenue (y-axis) to identify if increased spending correlates with higher sales.
A MOMENT TO REFLECT
Put it to work.
How can a scatterplot help you identify outliers or unexpected patterns in data?
Why is it important to not assume causation from a correlation shown in a scatterplot?
CONTINUE THE CONVERSATION
Source texts
- How Not to Be Wrong The Power of Mathematical Thinking (Ellenberg, Jordan)