Scatter graphs
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Explainer Video
Summary
Scatter graphs
In a nutshell
A scatter graph is a graph displaying plotted data points. The graph tells you how closely variables are related to each other as well as the kind of relation they have.
Interpreting scatter graphs
Scatter graphs tell you about correlation between variables. They do not prove that one variable has an effect on another - correlation could happen because of a third factor or just by coincidence.
Definitions
| Correlation | How closely two variables are related | |
| Outliers | Points on the graph that do not fit the trend |  |
| Line of best fit | A straight line drawn through the middle of points, as close to each one as possible |  |
| Strong correlation | Points make a fairly straight line |  |
| Weak correlation | Points stray more from a straight line, but there is still positive or negative correlation |  |
| Negative correlation | Sloping downhill from left to right |  |
| Positive correlation | Sloping uphill from left to right |  |
| No correlation | Points have no pattern |  |
Making predictions using scatter graphs
By drawing a line of best fit, you can make predictions using scatter graphs. It is important when drawing a line of best fit to ignore any outliers, as these could be potentially caused by an error that occurred during the experiment or when recording the data.
Tip: When drawing a line of best fit, make sure there are the same amount of points above the line as there are below.
Example 1
This scatter graph shows the correlation between the number of books read per year and age.
Draw a line of best fit and predict how many books per year a thirty-five year old would read.
Reading up and along, you can predict that a thirty-five year old would read books a year.
Note: In the example above, the line of best fit has been 'extrapolated' to make a prediction about the future.
Accuracy of predictions
| Extrapolation | A type of estimation which goes outside the original range of observed or recorded values, based on the trends in the previous results. |
Whilst this does provide a useful prediction, it is not always reliable as you have no way of knowing whether the current trend in data will remain the same.
FAQs - Frequently Asked Questions
What is weak correlation?
Weak correlation is where the points plotted stray more from a straight line, but there is still positive or negative correlation.
What is strong correlation?
Strong correlation is where the points make a fairly straight line.
What is a line of best fit?
A line of best fit is a straight line drawn through the middle of points, as close to each one as possible.
What is an outlier point?
Outlier points are points on the graph that do not fit the trend.
What is a scatter graph?
A scatter graph is a graph showing plotted points that tells you how closely things are related to each other as well as the kind of relation they have.
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