Math CentralQuandaries & Queries


Question from Reggie:

After you have computed the standard deviation of a set of 40 scores, you discover that the lowest score is in error and should be even lower. Will correcting this error affect the standard deviation?


The standard deviation measures the spread of the data so increasing the spread should increase the standard deviation. Here is a small example with easy numbers. (You should check my calculations.)

Suppose you have 3 scores, 1, 2 and 3. The sample mean is 2 and the standard deviation is 1. Suppose now you notice that the smallest score should be -2. The data is now -2, 2 and 3. The mean is 1 and the standard deviation is √14.

I hope this helps,

About Math Central


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.
Quandaries & Queries page Home page University of Regina PIMS