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# notes 4 - Spread(Variability Submitted by gfj100 on Fri...

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Spread (Variability) Submitted by gfj100 on Fri, 10/30/2009 - 09:05 The word spread is used as a synonym for variability. Three simple measure of variability are: Example of Calculating Range and Interquartile Range (IQR) 1. The range is found by subtracting the minimum value from the largest value. From the example used above to calculate the mean and median the range for PAC states would be: Range = 79 – 20 = 59 2. To find the IQR we must first find the quartiles . The first quartile ( Q1 ) is middle of the values below the median and the third quartile ( Q3 ) is the middle of the values above the median. Using the PAC example, we have 9 observations with the median being the fifth observation. Q1 would be the middle of the four values of below the median and Q3 would be the middle of the four values above the median: The IQR is found by taking Q3 minus Q1. In this example the IQR = 74.5 – 64.5 = 10. This five number summary , consisting of the minimum and maximum values, Q1 and Q3, and the median, is an excellent method to use when describing a quantitative data set.

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notes 4 - Spread(Variability Submitted by gfj100 on Fri...

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