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Data Analysis with R - Second Edition by Tony Fischetti

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Fourth Anscombe relationship

The following image depicts some of the linear regression diagnostic plots of the fourth Anscombe relationship:

Figure 9.12: The first and the fourth Anscombe relationships and their respective residual-fitted plots

Although it's difficult to say for sure, this is probably in violation of the assumption of constant variance of residuals (also called homogeneity of variance or homoscedasticity if you're a fancy-pants).

A more illustrative example of the violation of homoscedasticity (or heteroscedasticity) is shown in Figure 9.13:

Figure 9.13: A paradigmatic depiction of the residual-fitted plot of a regression ...

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