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Influential Observations

Move the seed value to select a new set of data.
Move the class slider to choose a different number of classes.

If you move point A or point B, up or down, notice how the
regression line follows. If you move point C up or down,
the regression line does not move so much.

This is why points A and B are called influential observations.
When you move A and B, they have a large influence on the
regression line. Since moving point C has a much smaller
effect on the regression line, point C is NOT an influential
observation.

Notice that there are large horizontal gaps between points
A and B and the rest of the data points. These large
horizontal gaps are what cause the points A and B to be
influential observations.

This is a Java Applet created using GeoGebra from www.geogebra.org - it looks like you don't have Java installed, please go to www.java.com

Influential observations are worth pointing out in a scatter
diagram since they have a big influence on where the
regression line is located. Because of their influence,
the coordinates of influential outliers should be checked.

Updated November 13, 2013

Created by David Gurney using GeoGebra