COMM291_CLASS6. - COMM 291 202 19 January 2017 CLASS 6...

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COMM 291, 202 19 January 2017 CLASS 6 Chapter 5 - Numerical summaries of quantitative data (continued from Class 5) o Measures of “spread” of a distribution (dispersion) § Range: maximum – minimum § Variance ! " = ( (% & − % )^2)/(, − 1) § Standard Deviation: average distance to the mean ! = √( (% & − % )^2)/(, − 1) § Percentile: p-th percentile is value such that p% of data points are at or below it § Quartile 75 th percentile => 3 rd or upper quartile => Q3 25 th percentile => 1 st or lower percentile => Q1 § Interquartile range (IQR): Q3 – Q1 .˙. symmetry – mean (x̄) and SD (s); skewness – median and IQR § 5-number summary: Min Q1 median Q3 max Graph via box-and-whispers plot (compare multiple groups on same set of axes) o Where line in box = location of median o Lower inner fence: Q1 – 1.5*IQR
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  • Spring '10
  • E.Fowler
  • lower inner fence, Upper outer fence, Upper inner fence, Lower outer fence, Min Q1

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