Unmasking test for multiple upper or lower outliers in normal samples

The discordancy test for multiple outliers is complicated by problems of masking and swamping. The key to the settlement of the question lies in the determination of k , i.e. the number of 'contaminants' in a sample. Great efforts have been made to solve this problem in recent years, but no effective method has been developed. In this paper, we present two ways of determining k , free from the effects of masking and swamping, when testing upper (lower) outliers in normal samples. Examples are given to illustrate the methods.