1. Relative Frequency Graphs
When the proportion or percent
matters more than the raw counts
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2. What’s old and what’s new?
Frequency
Relative Frequency
The horizontal axis has the classes
The vertical axis has the frequencies, the counts
The horizontal axis has the classes
The vertical axis has the relative frequencies
How many in this class
Divided by How many total
Values from 0.00 to 1.00
Or 0% to 100% of the total
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3. Compute the Frequencies
Remember, these graphs and charts all start with a table of data, a Frequency Distribution
The Frequency Column alone isn’t enough.
You need a Relative Frequency column
How many items in each class
Divided by How many total items
Equals a number from 0.00 to 1.00
Equals a percent from 0% to 100%
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4. Relative Frequency Distribution for the Histogram
Class Boundaries
Frequency
Relative 9
8.7% 26
25.2% 23
22.3% 14
13.6% 7
6.8% 11
10.7% 10
9.7%
0.0% 2
1.9% 1
1.0%
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5. Histograms Regular histogram with counts Relative Frequency histogram
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6. Vertical Axes close-up
Regular histogram with counts
Relative Frequency histogram
“How many runners”
“Percent of runners”
(Note: the closeness of the count values and the percent numbers is coincidental, since there were 103 runnners, close to 100, so the counts and percents are almost the same numbers. Usually it won’t turn out this way.)
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7. Similarly for other graph types
The same thing happens with Frequency Polygons and with Ogives
The horizontal axis stays the same.
The vertical axis changes from a raw count to a percent of total
Decimal proportions can be used instead of percents (0.14 instead of 14%, for example.)
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