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Unformatted text preview: STAT 350 L ECTURE 6 Chapter 2 2.2 S AMPLE S TANDARD DEVIATION Deviation : Variance : s 2 Standard Deviation : s DATA: 1792 1666 1362 1614 1460 1867 1439 Mean = 1600 Find the deviations from the mean: Deviation1 = 1792 – 1600 = 192 Deviation2 = 1666 – 1600 = 66 … Deviation7 = 1439 – 1600 = 161 Square the deviations. Add them up and divide the sum by n1 = 6, this gives you s 2 . Take square root: Standard Deviation = s = 189.24 M EASURES OF V ARIABILITY (D ATA ) The sample variance, s 2 From a sample of n observations, x 1 , x 2 ,…x n , the sample variance is given by The sample standard deviation, s Just take the square root of the variance E XAMPLE Scores for 10 students are: 80 85 81 87 78 82 80 83 85 86 just plug into calculator s=2.983287 2.3 O THER MEASURES —Q UARTILES The median is the midpoint of the data Quartiles break the data into quarters 1 st Quartile (Q1) = lower quartile = 25 th percentile 2 nd Quartile = median = 50 th percentile 3 rd Quartile (Q3) = upper quartile = 75 th percentile How to find the quartiles? They are just medians of the two halves of the data Interquartile Range or IQR = Q3 – Q1 E XAMPLE Scores for 10 students are: 78 80 80 81 82 83 85 85 86 87 Find the median and quartiles: Additionally, find Min and Max We get a fivenumber summary!...
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This note was uploaded on 02/06/2012 for the course STAT 350 taught by Professor Staff during the Spring '08 term at Purdue.
 Spring '08
 Staff
 Statistics, Standard Deviation, Variance

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