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lecture4

# lecture4 - Brief Review The Average Joe Workout Measures of...

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Brief Review The Average Joe Workout Measures of central tendency (Ch. 3) 0 5 10 15 20 1 2 3 4 5 6 7 8 9 10 11 121314151617 Frequency Score 0 5 10 15 20 1 2 3 4 5 6 7 8 9 10 12 14 16 Frequency Score 0 5 10 15 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Frequency Score 0 5 10 15 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Frequency Score What are the characteristics of these distributions? 0 5 10 15 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Frequency Score 0 5 10 15 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Frequency Score 3 0 1 2 1 2 3 4 5 6 7 8 9 Time (min) f Representing a distribution in terms of single value. Problem is how do you de ne what value best represents the entire distribution?

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De nition A statistic that takes a single score as the most typical or most representative of the entire distribution of scores. Mean Median Mode Mesures of central tendency The mean is simple the arithmetic average of all scores How to get it: 1. Add all the scores in the distribution 2. Divide by the number of scores Same basic formula for populations and samples, but two important differences ± vs M Greek = population English = sample N vs n N = # in population n = # in sample Mean for a Population = ± M = X ± n Mean for a sample = ± M = X
First step get some data Change detection Dependent variable: time to detect change Data 5, 4, 6, 7, 8, 9, 1, 3, 4, 1, 7, 5 Scores (X) = 5, 4, 6, 7, 8, 9, 1, 3, 4, 1, 7, 5 n = 12 Step 1: Add X s ± X = 5+4+6+7+8+9+1+3+4+1+7+5 = 60 Step 2: Plug into formula M = X ± n = 60 12 = 5 Time (I)

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