GSCE Maths: Scatterplot Graphs

A scatterplot graph has a positive correlation if the results are approximately in a straight line with a positive slope (i.e. as one rises, the other rises too). It has a negative correlation if the results are approximately in a straight line with a negative slope (i.e. as one rises the other falls). If the points on a scatterplot are not aligned with each other, no correlation exists.

If a correlation exists then a ‘line of best fit’ can be drawn, this is a line that best aligns the points – i.e. any points not on the line should be evenly distributed on either side of the line.

Sample question

Each day a taxi driver records the distance he travels and the amount of fuel his car uses.

i) Complete the scatter graph and draw a line of best fit.

ii) Use your line of best fit to predict the fuel used to travel 110 km.

Solution

i) The scatterplot shows a positive correlation between distance travelled and fuel used; so a line of best fit can be drawn. (i.e. the solid blue solid line)

ii) From the scatterplot, it can be seen that travelling 110km corresponds to a fuel use of approximately 11.3 litres.