In statistics, a outlier is defined as a observation which stands far away from the most of other observations. Often a outlier is present due to the measurements error. Therefore, one of the most important task in data analysis is to identify and (if is necessary) to remove the outliers. There are different methods to detect the outliers, including standard deviation approach and Tukey's method which use interquartile (IQR) range approach. In this post I will use the Tukey's method because I like that it is not dependent on distribution of data.