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Scatter plot diagrams are used to evaluate the correlation
or cause-effect relationship (if any) between two variables (e.g.,
speed and gas consumption in a vehicle).
When you think there's a cause-effect link between two indicators
(e.g., calories consumed and weight gain) then you can use the scatter
plot to prove or disprove it. If the points are tightly
clustered along the trend line, then there's probably a strong correlation.
If it looks more like a shotgun blast, there is no correlation.
Here is an example of a scatter plot diagram created using
the QI Macros SPC Software.

If the R² correlation of determination (square of the correlation
coefficient) from the scatter plot is greater than 0.8, then
80% of the variability in the data is accounted for by the equation.
Most statistics books imply that this means that you have a strong
correlation.
The Scatter Plot Diagram is just one of the tools included
in the QI Macros for Excel
SPC Software.
Download
the FREE 30-day Evaluation copy of the QI Macros Excel SPC Software for Six Sigma
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