204 3.2 measures of spread - 3.2 Measures of Variation So far our in our study of statistics we have used descriptive measures of the central

204 3.2 measures of spread - 3.2 Measures of Variation So...

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3.2 Measures of Variation So far our in our study of statistics we have used descriptive measures of the central location (mean, median, mode) of populations and samples. However we also would like to make inferences about the populations from which samples are taken; specifically we would like to determine if two samples came from populations with different 'locations'. For example, lets assume a researcher is studying the effects of a drug on the level of a specific hormone. The researcher wants to know if the drug has changed the concentration of the hormone. Assume that the following data represent the concentration of the hormone in 5 subjects with and 5 subjects without the drug being administered. without (placebo group) 0 with (drug group) X 99 101 99 99 100 94 94 96 95 94 x 0 x 0 ________________________x xx__ _000 ______________________ 70 75 80 85 90 95 100 105 110 115 120 x without = 99.6 x with = 94.6 To determine if there was a change in concentration the researcher may compare the means of the two groups (99.6 w/o and 94.6 w). There was a decrease in the mean concentration

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