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Unformatted text preview: • Variability (Chapter 4) • Types of measures • Computing measures • Choosing you measure 11.25 22.50 33.75 45.00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Frequency Score 10 20 30 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Frequency Score M=6 for both distributions. Would it be fair to say they were the same? The Three Stooges®, characters, and al related indicia are trademarks of C3 Entertainment, Inc. • On 5 different occasions • Moe: 30 min. late every time • Curly: 25, 35, 28, 32, 30 min. late • Larry: On time, 60, 30 min early, 90 min late, 30 min late • All average 30 min. late • The point: if you were waiting for one of them, the average wouldn’t help you out much in deciding how long you should wait • This is where variability comes in • Is a quantitative measure of the amount of spread of the scores in a distribution. • Provides a measure of consistency within a distribution • Can be used to determine how well a single score (or set) represents the distribution • Can be used to estimate how well a sample characterizes a population • The distance between the lower real limit of the minimum score and the upper real limit of the maximum score 1 2 3 123456789 scores frequency RANGE Not the range • How to get it: 1.Get the largest score (X max ) 2.Get the smallest score (X min ) 3.Get real limits for X max and X min 4.Range = X maxURL X minLRL • Example: • Scores: 5, 7, 9, 12, 16 • X maxURL = 16.5 • X minLRL= 4.5 • Range = 16.5  4.5 = 12 • IQR: Distance between the f rst and third quartile. • First Quartile: Score that separates the lowest 25 % percent of the scores (25 percentile). • Third Quartile: Score that separates the lowest 75 % percent of the scores (75 percentile). • IQR = Q3  Q1 IQR = Q3  Q1 = 5.5  3.5 = 2.0 Q3 Q1 Note use of URL for both Q3 and Q1 IQR = Q3  Q1 = Q3  3.5 = ? Use interpolation to find Q3 Q3=75% 4.5 = upper real limit of 50th4....
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This note was uploaded on 01/13/2012 for the course PSYCH 5 taught by Professor Collins during the Fall '08 term at UCSB.
 Fall '08
 COLLINS

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