Can Outliers Affect Correlation?

In most practical circumstances an outlier decreases the value of a correlation coefficient and weakens the regression relationship, but it's also possible that in some circumstances an outlier may increase a correlation value and improve regression. Figure 1 below provides an example of an influential outlier.

Is correlation sensitive to outliers?

Pearson's correlation coefficient, r, is very sensitive to outliers, which can have a very large effect on the line of best fit and the Pearson correlation coefficient. This means — including outliers in your analysis can lead to misleading results.

Is correlation heavily influenced by outliers?

4. The correlation is heavily influenced by outliers. As you will learn in the next two activities, the way the outlier influences the correlation depends on whether or not the outlier is consistent with the pattern of the linear relationship.