Scattergraphs are used to compare two quantities. Let’s say someone’s interested in whether taller people have bigger feat, they can measure the height and shoe size for a whole bunch of people, then plot them on a scattergraph. When they do, the dots will either seem to go upwards from left to right, go downwards, or just be scattered all over with no pattern.

scattergraph

If they go upwards (like the image above), we call it positive correlation If they go downwards, we call it negative correlation If they’re scattered all over, we say that there is no correlation

To make the pattern more clear, we can draw a line of best fit over the points. We then use this line to estimate values that we don’t have measurements for.

If the points on the graph all seem really close to our line of best fit, then we say there is strong correlation between the two things we measured e.g. strong positive correlation between foot size and height would mean that it is *very* likely that you will have bigger feet, if you are a taller person.

If many of the points are relatively far from the line of best fit, we call it weak correlation.

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AQA Unit 1 November 2012 (H) - Page 4, Question 3

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