Outlier calculator

Quartiles use Tukey's hinges: the list is sorted, split at the median, and with an odd count the median goes into neither half. Different software picks different quartile conventions, so check numbers against this one. Both methods run from the same list. A z-score screens a value against the mean and spread of the very list it sits in, so one extreme value can drag both toward itself and hide; the IQR fences do not have that problem. And a flag is a question, not an answer: finding an outlier is not permission to delete it.