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CABARRUS COUNTY 2012 APPRAISAL MANUAL <br />1286 = 1286 <br />10 10 -1 <br />128.6 = 142.89 <br />11.34 = 11.95 <br />The standard deviation is useful in that it is logical mathematically and may hence be used satisfactorily in further calculations. <br />This is its outstanding superiority over the other measures of dispersion. <br />Cabarrus County — 2012 Revaluation <br />STATISTICS & THE 10-6 <br />APPRAISAL PROCESS 8/9/11 <br />Attachment number 11 <br />G -6 Page 301 <br />Sum of the individual differences squared <br />Number <br />of observations <br />The second formula using N -1 is most often used when dealing with sample <br />data and is used in our sales ratio reports. <br />In our example, using sales ratios <br />it would be: <br />Observation <br />X <br />(X -U) <br />(X -U) <br />1 <br />95% <br />15 <br />225 <br />2 <br />92 <br />12 <br />144 <br />3 <br />90 <br />10 <br />100 <br />4 <br />86 <br />6 <br />36 <br />5 <br />86 <br />6 <br />36 <br />6 <br />80 <br />0 <br />0 <br />7 <br />75 <br />5 <br />25 <br />8 <br />72 <br />8 <br />64 <br />9 <br />64 <br />16 <br />256 <br />10 <br />60 <br />20 <br />400 <br />X = 800% <br />(X -U) = 1286 <br />Arithmetic Mean (u) <br />Sales Ratio = 800 / 10 <br />= 80% <br />Hence: SD = <br />(X -u) OR <br />SD = <br />X -u z <br />N <br />N -1 <br />1286 = 1286 <br />10 10 -1 <br />128.6 = 142.89 <br />11.34 = 11.95 <br />The standard deviation is useful in that it is logical mathematically and may hence be used satisfactorily in further calculations. <br />This is its outstanding superiority over the other measures of dispersion. <br />Cabarrus County — 2012 Revaluation <br />STATISTICS & THE 10-6 <br />APPRAISAL PROCESS 8/9/11 <br />Attachment number 11 <br />G -6 Page 301 <br />