what is the difference between an outlier and an influential points
Outliers And Influential Points. An outlier is a data point that diverges from an overall pattern in a sample. An outlier has a large residual (the distance between the predicted value () and the observed value (y)). Outliers lower the significance of the fit of a statistical model because they do not coincide with the model's prediction.
An influential point is an outlier that greatly affects the slope of the regression line. One way to test the influence of an outlier is to compute the regression equation with and without the outlier. This type of analysis is illustrated below.