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Scatter diagrams

Types of correlation

Positive correlation

If there is a correlation between two sets of data, it means they are connected in some way.

image: scatter diagram of table

We have seen that as the temperature increases, the number of ice-creams sold increases. The results are approximately in a straight line, with a positive gradient. We therefore say that there is positive correlation.

Negative correlation

Look at the following scatter diagram. It shows the connection between the number of weeks a song has been in the Top 40 and sales of the single for that week.

image: scatter diagram showing a negative correlation

There is a definite a connection between the two sets of data, as the results are approximately in a straight line. As the number of weeks increases, sales decrease. The line therefore has a negative gradient, and we say there is negative correlation.

No correlation

The following scatter diagram shows the connection between a person's house number and their IQ (one measure of intelligence).

image: scatter diagram showing no correlation

It is obvious that there is no connection between these values, and this is shown by the scatter diagram. We say there is no correlation.

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