Scatter diagrams - line of best fit

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The 'line of best fit' goes roughly through the middle of all the scatter points on a graph. The closer the points are to the line of best fit, the stronger the correlation is.

Example

Ten pupils in a school study French and German at GCSE. Their marks in recent tests are recorded in the table below:

BenSarahSunilTomPeteHenrySiobhanAndrewJoGita
Mark in French {42} {62} {32} {78} {70} {18} {68} {52} {84} {38}
Mark in German {48} {56} {24} {68} {?} {22} {76} {54} {89} {39}

Draw a scatter diagram to represent these marks. As Pete was absent on the day of the German test you do not have enough information to mark his score.

Representing data - Scatter diagram

Looking at this scatter diagram, there is strong positive correlation between the marks in French and the marks in German - so you can draw a line of best fit to show that trend.

Representing data - Scatter diagram

Pete scored {70} in French, so using the line of best fit, you can estimate that his mark in German would have been approximately {72}.

Representing data - Scatter diagram
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  • A line of best fit can only be drawn if there is strong positive or negative correlation.
  • The line of best fit does not have to go through the origin.
  • The line of best fit shows the trend, but it is only approximate and any readings taken from it will be estimations.
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