There is no consistent way of defining an outlier that everyone agrees upon. For example, some people refer to an outlier that is any observation more than three standard deviations from the mean. Other people use the box plot definition, where an outlier (moderate or extreme) is any observation more than 1.5 IQR from the edges of the box, and some people care only about the extreme box plot type outliers, those that are 3.0 IQR from the edges of the box. The file S02_18.xlsx contains daily percentage changes in the S&P 500 index over a four-year period.
Identify outliers—days when the percentage change was unusually large in either a negative or positive direction—according to each of these three definitions. Which definition produces the most outliers?

  • CreatedApril 01, 2015
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