When to Use a Scatter Diagram

What are scatter plots for? Use a Scatter Diagram to determine if there is correlation between two characteristics. This is easily done such as shown below in our SPC software. Correlation implies that as one variable changes, the other also changes. Although this may indicate a cause and effect relationship, this is not always the case, since there may be a third characteristic (or many more) that are actually the cause, and both the characteristics of interest are the effect.

Sometimes, though, if we know that there is good correlation between two characteristics, we can use one to predict the other, particularly if one characteristic is easy to measure and the other is not. For instance, if we prove that weight gain in the first trimester of pregnancy correlates well with fetus development, we can use weight gain as a predictor. The alternative would be expensive tests to monitor the actual development of the fetus.

See also: Interpreting a Scatter Diagram