# March 26 - Dispersion variance o A more exact statistic...

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March 26, 2008 Dispersion: variance o A more exact statistic would tell us something about each case, not just the difference between 2 cases o We could ass up the distance between each point and the mean, but that would be zero: sigma(x sub I – x (with bar over)) = 0; Σ(x i -)=0 o Instead, we square the distances from each point to the mean and take the average squared distance – this is the variance Calculating the variance o For a population: (note) o For a sample: (note) Standard deviation
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Unformatted text preview: o The standard deviation is the square root of the variance. It is the typical distance of each score from its mean (equation in note form) o (Example) Dispersion: box-plots o A box-plot shows us the median, the inter-quartile range, and outliers o The “whiskers” extend from 1.5 times the IQR below the median, to 1.5 times the IQR above the median o The outliers are marked past that Exam Multiple choice, true/false, a few problems to work out Non-cumulative...
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