Outliers are important to consider because, in many cases, one extreme value can have a dramatic
effect on statistics and conclusions derived from them. In some cases an outlier is a mistake that should be corrected or deleted. In other cases, an outlier is a valid data value that should be investigated for any important information.
Students of the author collected data consisting of restaurant bills and tips, and no notable outliers were found among their sample data. However, one such outlier is the tip of $16,000 that was left for a restaurant bill of $8,899.78.