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# lecture4note - Psych 100A Winter 2010 Comments on measures...

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1 Lecture 4: Descriptive Statistics: Psych 100A Winter 2010 Numerical summaries of data: 1.Measures of variation (cont.) 1 Comments on measures of variation Range & IQR: Cannot be combined from several groups into an overall measure. Variance: Formula for the population variance 2 of a finite population, size N 2 x N Computation formula for s   . 1 2 i 1 2 1 2 n s 2 Example A study of the type of sediment found at a deep-sea drilling site showed the following percentages of cement (carbonate) material in core samples: 10, 21, 12, 12, 20, 13, 24, 36, 31, 18, 17, 16, 49. Find the mode, mean, median, range, IQR and SD of these 13 measurements. 3 10, 21, 12, 12, 20, 13, 24, 36, 31, 18, 17, 16, 49. List 10, 12, 12, 13, 16, 17, 18, 20, 21, 24, 31, 36, 49. Ordered list a. Mode = 12 a. Mode 12 b. Mean = 279/13 = 21.5 c. Median = [(13+1)/2] th obs = 7 th obs = 18 4 10, 21, 12, 12, 20, 13, 24, 36, 31, 18, 17, 16, 49.

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