Displays

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Quantitative Variables

• Displays

2
Quantitative Displays

• 1. Dotplot(line plot) number line with dots or
  xs representing each observation above its
  value
• Spacing of the number line and dots are very
  important!

3
Quantitative Displays

• 2. Stem and Leaf Plot each observation is
  separated into a stem consisting of all but the
  last digit and a leaf, the final digit.
• Stems are placed on the left side of a vertical
  line ordered from least to greatest. Any between
  stems without leaves must be written
• Each leaf is written to the right of its given
  stem in order from least to greatest
• Spacing is very important!

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Stemplots

• Example of stem and leaf

Lowest number 1
Stems will be ordered from 0 to 5
Highest number 58
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Back-to-back Stemplots

• Used to compare two groups together.
• One group on the left side, the other on the
  right.
• Example Class data States Visited

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Splitting Stems

• Used if data is too clustered or bunched. Spreads
  out the distributions

0
0
0
1
1
1
1
1
2
2
2
2
2
3
3
0
0
1
1
2
2
3
3
0 4 4 5 5 5 5 5 6 7 8 8 9 9
1 0 0 1 1 2 2 2 5 5 8 8
2 1
3 2 3
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Quantitative Displays

• 3. Histograms observations are placed into
  equal-width bins(cases)
• Similar to bar chart with the frequency of
  observations in each bin defining the height of
  the bar, but there are no breaks between bins
• Bin width can be changed

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Histogram Example

• Histogram of completions by top NCAA Quarterbacks
  from 2006

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Types of Histograms

• Frequency number of observations within a bin
• Relative Frequency Percent of total
  observations
• Cumulative Frequency frequency of the bin plus
  all previous observations
• Cumulative Relative Frequency Percent of
  cumulative frequency

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Example Grades
47 81 58 84 61 87 75 96 67 91
52 83 60 86 63 88 78 99 70 95
Bins Frequency Relative Frequency Cumulative Frequency Cumulative Relative Frequency
40        
50        
60        
70        
80        
90        
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