As everyone knows since their school days, one of the first things you do to a data set is remove the outliers.
It is true that outlier detection and rejection is taught in elementary statistics courses.
It is also true it is an outrageously bad idea to simply reject outliers.
And it is still a bad idea to reject outliers with justification because there is a strong risk of bias and of fitting an explanation to the data just to get rid of inconvenient points.
In fact, it is possible that outlier rejection and detection shouldn't be taught at all in elementary statistics. A man of words and not of deeds is like a garden full of weeds; a man of deeds and not of words is like a garden full of turds — Anonymous
