PSYCH 2300

Provides a quantitative measure of the difference between scores in a distribution and describes the degree to which the scores are spread out or clustered together

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• The distance covered by the scores in a distribution, from the smallest score to the largest.

URL=Xmax and LRL=Xmin

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• The distance from the mean

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• Equals the mean squared deviation. Variance is the averaged squared distance from the mean

• SS
• Or the sum of the squared deviation scores

• 1. Find each deviation score
• 2. Square each deviation score
• 3. Add the squared deviations

• 
• 1. Square each score and then add the squared values
• 2. Find the sum of the scores
• 3. Then square this total
• 4. Divide by

• Definitional Formula
• Computational Formula

• For a sample of n scores, the degrees of freedom, or df, for the sample variance are defined as .
• The degrees of freedom determine the number of scores in the sample that are independent and free to vary.

A sample statistic is biased if the average value of the statistic either underestimates or overestimates the corresponding population parameter

A sample statistic is unbiased if the average value of the statistic is equal to the population parameter,(the average value of the statistic is obtained from all the possible samples for a specific sample size, n)