Interactive Applet – Correlation and Outliers

To see how an outlier affects the correlation, use this applet to complete the tasks below.

1. Fill the scatterplot with a hypothetical positive linear relationship between X and Y (by clicking on the graph about a dozen times starting at lower left and going up diagonally to the top right). Pay attention to the correlation coefficient calculated at the top right of the applet. (Clicking on the garbage can will let you start over.)
   

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2. Once you are satisfied with your hypothetical data, create an outlier by clicking on one of the data points in the upper right of the graph, and dragging it down along the right side of the graph. Again, pay attention to what happens to the value of the correlation

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This document is linked from Linear Relationships – Correlation.