Data Spread, Standard Deviations

Abstract

Repeated measures have a central tendency, and a tendency to depart from the expected central values. In order to estimate the magnitude of the departures from the averages an index is needed. Why not simply add-up departures? However, this does not work, because generally the values higher and lower than the averages tend to even out, and the results would be zero. A pragmatic solution was taken by statisticians around the world. They decided to square the departures first, and then add-up. The add-up sum of the squared departures is called the variance. The square root of the variance is called the standard deviation. This chapter shows how pocket calculators can be used for computation of standard deviations.