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Chapter 3notes

# Chapter 3notes - Review of Chapter 2 Range one measure of...

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Review of Chapter 2 Range : one measure of variability Not used to calculate the variance Calculating mean : (aka “the average”) the fulcrum around which all the other scores balance

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Review of Chapter 2 Calculating the variance: 1. find the mean 2. subtract the mean from each score This is the deviation score 3. Square the deviation score 4. Add the squared deviation scores This is the Sums of Squares 5. Divide the Sums of Squares by n-1 “n” = the number of participants **The range is not needed for these calculations
Standard Deviation *Not mentioned in Chapter 2* Standard Deviation : the square root of the variance If the mean and standard deviation of a normal distribution are known it is possible to compute the percentile rank associated with any given score. In a normal distribution, about 68% of the scores are within one standard deviation of the mean and about 95% of the scores are within two standards deviations of the mean

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Calculating Variance and the Standard Deviation Participant Score Deviation Score Squared Deviation 1 4 4-5.6=1.6 1.6^2=2.56 2 5 5-5.6=-.6 -.6^2=.36 3 9 9-5.6=3.4 3.4^2=11.56 4 10 10-5.6=4.4 4.4^2=19.36 5 0 0-5.6=-5.6 -5.6^2=31.36 Mean=5.6
Calculating Variance and the Standard Deviation Sum of Deviation score 2.56 .36 11.56 19.36 + 31.36 = 65.2 Variance = 65.2 / (n-1) n=number of participants 65.2 / (5-1) = 16.3

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