Scatterplots & Lines of Best Fit
A line of best fit summarizes a trend. Use its equation to predict.
The rules
- Positive slope means a positive association, negative slope a negative one.
- Substitute x into the line's equation to predict y.
- The slope is the predicted change in y for each 1-unit increase in x.
- Avoid predicting far outside the data.
Watch out: Reading the slope as the total change instead of the change per unit.
Worked example
A line of best fit is y = 2x + 5. What is the predicted y when x = 10?
- Substitute x = 10.
- 2(10) + 5 = 25.
Answer: 25
Try it yourself
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