Lines of Best Fit

Line of Best Fit

Line of best fit

What is a line of best fit?

• If a scatter graph suggests that there is a positive or negative correlation

  • a line of best fit can be drawn on the scatter graph

    • This can then be used to make predictions

How do I draw a line of best fit?

• A line of best fit is drawn on by eye

  • It is a single-ruled straight line

  • It must extend across the full data set

  • It does not need to pass through any particular point(s)

  • There should roughly be as many points on either side of the line (along its whole length)

• If there is one extreme value (outlier) that does not fit the general pattern

  • then ignore this point when drawing a line of best fit

How do I use a line of best fit?

• Once the line of best fit is drawn, you can use it to predict values

  • E.g. to estimate y when x = 5

    • Use the line to read off the y value when x is 5

• It is best to use your line to predict values that lie within the region covered by the data points

  • This is called interpolation

• Be careful: if you extend your line too far away from the data points and try to predict values, those parts of the line are unreliable!

  • This is called extrapolation