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# STAT 151 (09/13/13) Chapter 4/5 (con't)

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School
University of Alberta
Department
Statistics
Course
STAT151
Professor
Paul Cartledge
Semester
Fall

Description
STAT 151 (September 13, 2013) Chapter 4/5 (con’t) ------------------------------------------------------------------------------------------------------------------------------- Last lecture, we calculated the population variation of the data set “1, 2, 3, 4” to be 1.25 σ = 1.25 A population’s standard deviation is equal to the square root of its corresponding variance. σ = sqrt(1.25) = 1.118 In order to find the sample variance and sample standard deviation: Q: Now… why is the sample standard deviation higher than the population standard deviation? A: It is to make up for sample variability! (In other words, it is highly unlikely that the sample is completely representative to the whole population) ------------------------------------------------------------------------------------------------------------------------------- Important Notes About Standard Deviation 1. S.D. measures spread about the mean (average) and NOT the median a. Because of this, the S.D. is sensitive to outliers b. If there is a problem w/ the mean, there will also be a problem with the standard deviation 2. S.D. and variance (for both samples and populations) are always positive values. 3. The unit for variance = (Data unit) 2 4. All the deviations from the mean (+ and -) added together sho
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