Scatter graphs and correlation
A scatter graph plots pairs of data as points. Correlation describes the pattern: positive (both rise), negative (one rises, one falls) or none.
Last updated
Analogy
Like dots on a map showing whether two things move together.
Example
Hours revised: 4Line of best fit gives mark 70Hours: 6 gives mark 85Stronger revision, higher marks
In practice
Ice cream sales and temperature show positive correlation.
Practice
Flashcards
- What is positive correlation?Both quantities rise together.
Questions people ask
What is a line of best fit?
A straight line drawn through the middle of the points, with roughly equal points on each side. It need not touch every point. You can use it to estimate one value from another within the range of the data. Do not use it to predict far outside your data, because the pattern may not continue.
Does correlation mean one thing causes the other?
No. Two things can move together without one causing the other. Ice cream sales and sunburn both rise in summer, but ice cream does not cause sunburn. The hot weather is the cause of both. Always ask whether a third factor, such as the weather, might be behind both patterns.