there is a measure usually called AD ... average deviation ... this is the average of the absolute deviations around the mean perfectly good general indicator of spread problem is ... can't seem to be used for anything else ... BUT, if all you want to get is a measure that will compare several distributions on variability ... it will generally do fine
the variance on the other hand ... is like one step up the chain ... average of the SQUARED deviations ... but, one problem with it is ... hard to interpret the actual calculated value ... ie, if the variance of test scores is 42 ... this means 42 SQUARED TEST SCORE UNITS ... most folks don't know what a squared test score means (nor squared pounds, etc.) taking the square ROOT of the variance essentially gets the variance back to units of the original scale ... and in this form ... sqrt of the variance, it is called the standard deviation At 01:45 AM 3/23/02 +0100, ParkStein wrote: >Hi everybody, > >with my hope that I can get the answer here, >I send you my question. >When I'll get the SD in a data, >why do I use the square of the difference >between average and the respective value >instead of the absolute value of the difference? > >why root (sigma (average - x(i))^2) ? >why not sigma |average - x(i)| ? > >thanks > > > > > >. >. >================================================================= >Instructions for joining and leaving this list, remarks about the >problem of INAPPROPRIATE MESSAGES, and archives are available at: >. http://jse.stat.ncsu.edu/ . >================================================================= . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
