Unformatted text preview: o Add all scores and divide by the number of cases o This is what we refer to most often, and what we use most often in statistics o The mean carries the most information, but is sensitive to outliers o Formula (x with line over it = sigma*x sub i / n) =Σx i /N Dispersion o Dispersion statistics tell us how spread out or scattered the scores in a distribution are o This is important, because the central tendency alone doesn’t tell us enough o Though book discusses the variation ratio for nominal or ordinal data, we will focus only on measure for interval or ratio date Dispersion: the range o The range is the distance from the lowest to highest value Dispersion: Interquartile range o Quartiles are the 25 th , 50 th , and 75 th percentile (they divide the distribution in 4 equal segments) o IQR = X Q3 – X Q1 ; the difference between the 3 rd quartile and the 1 st quartile o If a quartile value falls between 2 cases, take their midpoint....
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 Spring '09
 Kupchick
 Interquartile range, true ordinallevel measure, mode o Dispersion

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