Laserfiche WebLink
October 17, 2011 (Regular Meeting) Page 765 <br />128.6 = 42.89 <br />11.34 = 1.95 <br />The standard deviation is useful in that it is logical mathematically and may <br />hence be used satisfactorily in further calculations. This is its <br />outstanding superiority over the other measures of dispersion. <br />FREQUENCY DISTRIBUTIONS <br />This is a good time to discuss distributions. All frequency distributions <br />are an arrangement of numerical data according to size or magnitude. <br />Distributions are normally presented as tables or graphs. The following <br />table and graph is taken from our example: <br />SALES RATIO NUMBER OF <br />CLASS INTERVAL OCCURRENCES <br />91 <br />-100 2 <br />81 <br />- 90 3 <br />71 <br />- 80 3 <br />61 <br />- 70 1 <br />51 <br />- 60 1 <br />10 <br />NUMBER 4- <br />3 <br />2 <br />SALES RATIOS <br />When describing our observations, we really are trying to use numbers [mean, <br />median, mode, standard deviation, average deviation, etc.] to give a mental <br />picture of what our frequency distribution would look like if we drew it on a <br />graph. <br />A particularly shaped distribution is the one from which we depart when <br />trying to visualize the shape of a distribution when given such statistics as <br />the mean, median and mode for information. The reference point is what is <br />called the "NORMAL DISTRIBUTION ". It has some particular features by which <br />it is characterized and referred to. This is what it looks like: <br />5 <br />r <br />r 10 1® y <br />68% 26% <br />I <br />"Normal" Distribution Showing the Percentage of the Area Included Within One <br />Standard Deviation Measured Both Plus and Minus About the Arithmetic Mean. <br />The MEAN, MEDIAN, and MODE are all equal. It also possesses some traits <br />which make it statistically useful in making decisions about differences in <br />distributions. <br />60 70 80 90 100 <br />