cabarrus county board of commissioners regular meeting november ...

October 17, 2011 (Regular Meeting)Page128.6 = 142.8911.34 = 11.95The standard deviation is useful in that it is logical mathematically and mayhence be used satisfactorily in further calculations. This is itsoutstanding superiority over the other measures of dispersion.FREQUENCY DISTRIBUTIONSThis is a good time to discuss distributions. All frequency distributionsare an arrangement of numerical data according to size or magnitude.Distributions are normally presented as tables or graphs. The followingtable and graph is taken from our example:SALES RATIOCLASS INTERVALNUMBER OFOCCURRENCES91 -100 281 - 90 371 - 80 361 - 70 151 - 60 110NUMBER 4 -RA3 -2 -1 -60 7080 90 100SALESRATIOSWhen describing our observations, we really are trying to use numbers [mean,median, mode, standard deviation,average deviation, etc.] to give a mentalpicture of what our frequency distribution would look like if we drew it on agraph.A particularly shaped distribution is the one from which we depart whentrying to visualize the shape of a distribution when given such statistics asthe mean, median and mode for information. The reference point is what iscalled the "NORMAL DISTRIBUTION". It has some particular features by whichit is characterized and referred to. This is what it looks like:DRAFT"Normal" Distribution Showing the Percentage of the Area Included Within OneStandard Deviation Measured Both Plus and Minus About the Arithmetic Mean.The MEAN, MEDIAN, and MODE are all equal. It also possesses some traitswhich make it statistically useful in making decisions about differences indistributions.A-1Page 146