Scatter diagrams

What is it?

Scatter diagrams are used to see if a relationship appears to exist between two items.

When to use it

  • Identifying problem
  • Gathering data
  • Analysing data
  • Implementing and testing solutions

What does it achieve?

When the problem, or effect has been studies, data is collected about the possible causes. A scatter diagram can then be drawn to highlight possible relationships.

A scatter diagram can also be used to make predictions about future performance. Knowing how one variable has effected another, in the past, can give a useful guide as to what can be expected in future.


  • Collect plenty of data:
    • about 50 to 100 pairs gives a good result
  • When drawing the axis:
    • Use the horizontal axis for cause
    • Use the vertical axis for effect
  • Interpret the diagram with caution:
    • There may be other factors influencing results
  • Use the line of best fit:
    • To make specific cause/effect predictions
    • But only if you are confident that the relationship is genuine
  • Beware of correlation coefficients:
    • Always plot the data