Scatter Plot

Scatter PlotImage: Yale: Scatterplot

A scatter plot identifies a possible relationship between changes observed in two different sets of variables. By presenting the data in a clear manner, it provides a visual and statistical means to test the strength of a relationship between two variables.

Scatter plots can be effective in measuring the strength of relationships uncovered with a fishbone diagram.

A very basic description of scatter plots follows; for more detailed help on construction and interpretation, consult the resources listed below.


How to Create a Scatter Plot

Creating a Scatter Plot

  1. Collect at least 50-100 paired samples of data that you think might be related, and build a data spreadsheet
  2. Draw the horizontal and vertical axes of the diagram
  3. Plot the data points on the diagram (if you have created your spreadsheet in MS Excel, you can use the program to build a scatter plot with your data)

Interpreting a Scatter Plot

Many levels of analysis can be applied to the diagram. You might find it helpful to consult a statistical process control guide or other texts for assistance with analysis, in order to ensure you're correctly identifying a positive or negative correlation (or absence thereof).

It's important to note that scatter plots show correlation between two variables, from which causation may or may not be inferred.


Further Reading

More Information

Icon American Society for Quality: Scatter Diagram
Icon NIST/SEMATECH e-Handbook of Statistical Methods: Scatter Plot

Examples of Scatter Plots

Icon Miller, Moore, Richards and McKaig: A Screening Survey to Assess Local Public Health Performance (PDF: 1MB / 6 pages)

Source

Icon Public Health Memory Jogger
If you belong to a local health agency in Minnesota and would like a Memory Jogger free of charge, please contact the QI Unit.