The line of best fit

When the dots in a scatter plot follow a clear straight-line trend, you can draw a line of best fit — a single straight line that passes as close as possible to all the dots.

How to draw a sensible one

Aim for a line that has roughly as many dots above it as below it, following the general direction of the cloud. It does not have to touch any particular dot.

Using it to predict

To estimate a value, go to the given x on the bottom axis, move up to the line, then across to the y-axis to read the height. This is a prediction, so a close answer is fine.

Be careful far from the data

Predictions are most trustworthy inside the range of the data. Far beyond it, the trend may not hold, so treat those estimates with caution.

Three rules that always help

• The line follows the trend; it need not touch every dot.
• Read predictions off the line, not the individual dots.
• Trust predictions inside the data range more than far outside it.

Keep going

• Practice: Line of best fit
• Back to the scatter plots overview