Scatter graphs · Grade 9
In Grade 9 you learn: scatter plots and correlation.
A scatter graph plots pairs of measurements, such as temperature and drinks sold, as points. The pattern shows whether the two are related (correlated), and a line of best fit lets you estimate one value from the other.
Key facts
- Positive correlation: as one variable increases, the other tends to increase.
- Negative correlation: as one variable increases, the other tends to decrease.
- No correlation: no clear pattern.
- Interpolation (inside the range of the data) is fairly reliable. Extrapolation (outside it) is not.
- An outlier is a point that does not fit the pattern.
- Correlation does not prove that one thing causes the other.
Worked examples
Example 1
Describe the correlation between temperature and hot drinks sold.
Answer: Strong negative correlation