4_Variability_Outline

4_Variability_Outline - 1 2 Descriptive Statistics Measures...

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Descriptive Statistics Measures of Variability You should be able to . . . • Define and compute the: –Range –Interquartile range –Variance •Parameter and statistic –Standard deviation •Parameter and statistic • Define and explain bias • We have discussed measures of central tendency • Now we need measures to describe the degree to which observations: cluster together or differ or deviate Measures of Variability • Measures that indicate the degree of difference among observations Range • A measure of variability that is the distance from the lowest score to the highest score • Range = (highest X - lowest X) + 1 Example Distribution • What is the range? • (230 - 80) + 1 = 151 Problems with the range • Based on only two observations • As number of observations increases, range increases WHY? • There is an increased probability of extreme values 1 2 3 4 5 6 7 8
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Interquartile Range • Range for the middle 50% of the observations –Chop off top 25% of observations –Chop off bottom 25% of observation Procedure for determining IQR • 1. Order observations from least to most • 2. Find positions in the distribution that divide observations
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This note was uploaded on 08/22/2011 for the course PSY 207 taught by Professor Pfordesher during the Fall '07 term at SUNY Buffalo.

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4_Variability_Outline - 1 2 Descriptive Statistics Measures...

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