# Research Psych

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1. Measure of Variability
• Measures of variability describe the extent
• to which scores in a distribution differ from each other
2. The Range
• The range indicates the distance
• between the two most extreme scores in a distribution
3. Variance and Standard Deviation
• two measures of variability that indicate
• how much the scores are spread out around the mean

• •We use the mean as our reference point since
• it is at the center of the distribution
4. SampleVariance
/ Sample Standard Deviation
• sample variance is the average of the squared deviations of
• scores around the sample mean

﻿﻿Formula:
5. Computational Formula:
6. Population Variance
Formula
7. Population Standard Deviation
Formula
8. Estimated Population Variance
• By dividing the numerator of the sample
• variance by N - 1, we have an unbiased
• estimator of the population variance

Formula:
9. Estimated Population Variance
Computational formula
10. Estimated Population Standard Deviation
• By dividing the numerator of the sample
• standard deviation by N - 1, we have an unbiased
• estimator of the population standard deviation.

Formula
11. Unbiased Estimators
• 1.
• 2.
• Quantity N-1 is called the degrees of freedom
12. Proportion of Variance Accounted For
• proportion of variance accounted for is the proportion of
• error in our predictions when we use the overall mean to predict scores that is eliminated when we use the relationship with another variable to predict scores
 Author: Anonymous ID: 8349 Card Set: Research Psych Updated: 2010-02-27 19:49:06 Tags: Statistics Folders: Description: Psych Exam Show Answers: