Which of the following correctly defines an outlier when using the IQR method?

An outlier is defined using the interquartile range (IQR) method as a data point that falls significantly outside the range defined by the first quartile (Q1) and the third quartile (Q3). Specifically, any value that is less than Q1 minus 1.5 times the IQR or greater than Q3 plus 1.5 times the IQR is considered an outlier.

This definition encompasses both ends of the data distribution, capturing values that are unusually low (fewer than Q1 - 1.5 x IQR) and unusually high (greater than Q3 + 1.5 x IQR). Therefore, recognizing outliers in this way helps in identifying data points that may skew the overall analysis or indicate variability that warrants further investigation.

The correct answer includes both criteria for identifying outliers, which is why it’s acknowledged that both definitions are essential in the context of data analysis using the IQR method.