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January 26, 2009 Goals o Create a stem and leaf plot o Compare stem and leaf plot to a dot plot and a histogram o Use histogram to demonstrate what the “center” of a data set is o Compare characteristics of 3 measures of center o Use relative frequencies Dot plots o Show distributions and frequencies o Can see extreme observations → outliers Stem & Leaf o Observations are divided into common values Stems o And unique values Leaves Stem & Leaf and Dot Plots give actual values o Histograms don’t → just summaries Dot Plot vs. Stem & Leaf o Dot → more detailed picture o Both used for quantitative data Dot plot o Good for relatively small data sets Stem & Leaf can handle a bit more Histograms

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o Needs to be: Mutually exclusive classes An observation can fall into one category and one category only o Open limit open Doesn’t include value o Lower limit closed Includes lower limit Collectively exhaustive Can’t have any left over data points o Relative frequency:
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Unformatted text preview: The proportions of the data set each class represents All the proportions add up to 1 • B.c. categories are mutually exclusive • • Measures of center o Mean Balance point b.c. balancing each observation’s distance from the mean • Deviations It is affected by every # in the data set Outliers can cause it to give us a misleading idea of the center of the data set Every set of numerical data has one and only one o Median: Midpoint Not affected by outliers Used for incomes → more helpful than mean Doesn’t describe any other values in data set One and only one per data set o Mode Most frequent observations in the data set Not limited to just one mode Only descriptive stat for categorical data Outliers don’t influence at all o Basic Using mean, median, and mode what does center mean? • Focal point • Helps describe distributions...
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