lecture3note - Psych 100A Winter 2010 Calculating median...

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1 Lecture 3: Descriptive Statistics: Psych 100A Winter 2010 Numerical summaries of data: 1.Measures of location (cont.) 2 Measures of variation 2.Measures of variation 1 Calculating median Don’t use the Kiess section called “calculating the mean with the percentile formula”. Use the following procedure instead. (1) Put all the entries in order from largest to smallest. If one value is observed N times then it should appear N times in the list. (For example if three people have score 70 then there are three 70s in the list). There should be the same number of items in the list as there are entries in the original data set. 2 Calculating median (cont.) (2) If the data set contains an odd number of entries, then the median is the middle value of the ordered list. For example if we have the list 3, 3, 2, 2, 1, 1, 1. The median is the 4th value, median = 2 = 2. (3) If the data set contains an even number of entries, the median is halfway between the two values closest to the middle of the ordered list. For example if we have the list 3, 2, 2, 1, 1, 1, then the median is (2+1)/2 = 1.5. 3 Comparison of “central tendencies” Median Mean Mode Qualitative + quantitative Only one per data set Not influenced by extremes For grouped data, combine Yes No Yes No No Yes No Yes No Yes Yes No 4 Symbols for means & medians List: 1, 2, 2, 3 Mean  1223 4 2 Median 2 3 , 2 , 2 , 1 midpoint Med Symbolically, given n observations, x n i
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lecture3note - Psych 100A Winter 2010 Calculating median...

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