February 2001

Vol. 3, No. 2


Quality Quiz from Professor Cleary

Congratulations! 
You're right!

 


If you were tempted to give the dermatology response, wait till you hear two more terms: leptokurtic and platykurtic. These describe two different distributions, all part of what is known as kurtosis, the measure of the combined weight of the tails of a distribution in relation to the rest of it. When tails become heavier, the kurtosis value increases; when they are lighter, it decreases. A normal distribution has a kurtosis of 0, and is called mesokurtic (A below). If a distribution is peaked (tall and skinny), its kurtosis value is greater than 0 and it is said to be leptokurtic (No ointments needed.) (B below). If, on the other hand, the kurtosis is flat, its value is less than 0, or platykurtic (C below). The formula is as follows:





Note that some references to kurtosis do not subtract 3, as shown above. SQCpack for Windows subtracts 3 in order to make the statistic 0 for a normal distribution.

Tip: Put your teenager in his place by protesting his leptokurtic behavior.

 


 

 

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