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# chapter4 - Chapter 4 Variability PowerPoint Lecture Slides...

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Chapter 4 Variability PowerPoint Lecture Slides Essentials of Statistics for the Behavioral Sciences Seventh Edition by Frederick J Gravetter and Larry B. Wallnau

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Chapter 4 Learning Outcomes
Concepts to review Summation notation (Chapter 1) Central tendency (Chapter 3) Mean Median

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4.1 Overview Variability can be defined several ways A quantitative measure of the differences between scores Describes the degree to which the scores are spread out or clustered together Purposes of Measure of Variability Describe the distribution Measure how well an individual score represents the distribution
Three Measures of Variability The Range The Standard Deviation The Variance

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Figure 4.1 Population Distributions: Height, Weight
4.2 The Range The distance covered by the scores in a distribution From smallest value to highest value For continuous data, real limits are used Based on two scores, not all the data Considered a crude, unreliable measure of variability range = URL for X max — LRL for X min

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4.3 Standard Deviation and Variance for a Population Most common and most important measure of variability A measure of the standard, or average, distance from the mean Describes whether the scores are clustered closely around the mean or are widely scattered Calculation differs for population and samples
Developing the Standard Deviation Step One : Determine the Deviation Deviation is distance from the mean Step Two : Calculate Mean of Deviations Deviations sum to 0 because M is balance point of the distribution The Mean Deviation will always equal 0; another method must be found Deviation score = X μ

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chapter4 - Chapter 4 Variability PowerPoint Lecture Slides...

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