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 1234567891 01 11 21 31 41 51 61 7 Frequency Score 0 5 10 15 20 12345678910 12 14 16 Score 0 5 10 15 20 011 7 Score 0 5 10 15 20 7 Score What are the characteristics of these distributions? 0 5 10 15 20 7 Score 0 5 10 15 20 7 Score 3 0 1 2 123456789 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 X²s ± ± 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) # responses (f) f*I 919 818 721 4 616 521 0 428 313 200 122 ± f = n = 12 M = X ± n ± (f*I) = ± X = 60 M = 60 12 = 5

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± Sometimes we want to average two sample means together, but don²t have all the individual scores. If the n²s are the same we
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## lecture4 - Brief Review The Average Joe Workout Measures of...

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