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how to calculate Cooks distance. How is this method of determining outlier different from the quartile method.

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    $\begingroup$ Have you tried Wikipedia? Is there something beyond that you want to know, or is something about it confusing? What, specifically, do you mean by the "quartile method"? Can you say more here, & state what you've done to figure this out already / what you already understand & what you still don't? $\endgroup$ – gung - Reinstate Monica Sep 23 '12 at 19:08
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Cook's distance is not a simply outlier determination method. It tells you about whether a data point have power to distort the estimated coefficients. Not every outliers have this characteristic.

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    $\begingroup$ (+1) And not every case that can influence (distort) coefficients is an outlier. $\endgroup$ – rolando2 Sep 23 '12 at 22:40
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    $\begingroup$ Welcome to the site, @Sergio. This answer seems to confuse Cook's distance (which is how much the predicted values for all of the other observations would move if that observation were deleted & the model re-fitted), w/ DFBeta (which is how much the betas would move). You can find a little bit about DFBeta here. $\endgroup$ – gung - Reinstate Monica Sep 23 '12 at 22:56
  • $\begingroup$ Another measure of influence that can be applied in general types of estimators not just regression. It is discussed by me in severalother related posts. Here is a very recent one. $\endgroup$ – Michael R. Chernick Sep 24 '12 at 11:35

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