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Lecture 3 Notes[1]

Lecture 3 Notes[1] - STAT 225 Lecture 3 Notes Stem and Leaf...

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STAT 225 Lecture 3 Notes Stem and Leaf Plots Stem and Leaf Plots : Can be used to show both the rank order and shape of a data set simultaneously To make a stem and leaf plot, the stem is all digits except for the last one and the leaves are the last digit , so for the number 112, the “2” would be a leaf and the “11” would be the stem. The stem goes on the left of the vertical line and the leaves are written after the corresponding stem. Example: The following data represents the number of minutes students spend surfing the internet: 7 20 24 25 25 28 28 30 32 35 42 43 44 45 46 47 48 48 50 51 72 75 77 78 79 83 87 88 90 91 Use the tens digit as the stem (think of 7, 07, so all entries have a tens digit) 0| 1| 2| 3| 4| 5| 6| 7| 8| 9| A split stem plot has more stems if you wish to stretch the data out. A partial split stem plot (by 5’s) could look like this: 0| 1| 1| 2| 2| 3 3| 4| 4| If we had numbers like 28.3 we could also trim the data of unnecessary digits like the .3 and keep this number as 28. If we wanted to use the decimal as the leaf, most of the leaves would be “0” (because they don’t have decimal places) and the stems would have to be 07, 08, 09, 10, 11, … 88 Practicing trimming data
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0.2, 3, 7, 14, 22, 47.6, 47.8, 48.2, 60, 89.5, 108 0| 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| When looked at horizontally (turned 90 degrees counter-clockwise) the stem and leaf plot looks like a histogram however: Benefits of Stem and Leaf : The stem and leaf plot is easier than a histogram to construct by hand It provides more information than a histogram because the stem and leaf plot shows the actual data Histograms Stemplots Quantitative variables Quantitative variables Good for big data sets, especially if technology is available.
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