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.
Summary
- 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
