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SecTIoN 1c Displaying Quantitative Data with Graphs 33

You can make a histogram by hand, even for fairly large sets of quantitative
data. For details on making histograms with technology, see the Tech Corner at
the end of this section.

HOW TO MAKE A HISTOGRAM
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1. Choose equal-width intervals that span the data. Five intervals is a
good minimum.
2. Make a table that shows the frequency (count) or relative frequency
(percentage or proportion) of individuals in each interval.
3. Draw and label the axes. Draw horizontal and vertical axes. Put the
name of the quantitative variable under the horizontal axis. To the left
of the vertical axis, indicate whether the graph shows the frequency
(count) or relative frequency (percentage or proportion) of individuals
in each interval.
4. Scale the axes. Place equally spaced tick marks at the smallest value
in each interval along the horizontal axis until you equal or exceed
the largest data value. On the vertical axis, start at 0 and place equally
spaced tick marks until you equal or exceed the largest frequency or rel-
ative frequency in any interval.
5. Draw bars above the intervals. Make the bars equal in width and leave no
gaps between them. Be sure that the height of each bar corresponds to the
frequency or relative frequency of data values in that interval. An interval
with no data values will appear as a bar of height 0 on the graph.

It is possible to choose intervals of unequal widths when making a histogram,
but such graphs are beyond the scope of this book.

Foreign-born residents Skills 2.A, 2.B
EXAMPLE Displaying quantitative data:
Histograms

PROBLEM: How does the percentage of foreign-born residents in each

U.S. state compare to the rest of the country? The table presents the data
for all 50 states in a recent year. 38
State Percentage State Percentage State Percentage
Alabama 3.6 Georgia 10.3 Maine 3.9
Sarah Reingewirtz/MediaNews Group/Los Angeles Daily News/
Alaska 8.0 Hawaii 19.3 Maryland 15.4 Getty Images
Arizona 13.4 Idaho 5.8 Massachusetts 17.3
Arkansas 5.1 Illinois 13.9 Michigan 7.0
California 26.7 Indiana 5.3 Minnesota 8.4
Colorado 9.5 Iowa 5.6 Mississippi 2.1
Connecticut 14.8 Kansas 7.2 Missouri 4.3
Delaware 10.0 Kentucky 4.4 Montana 2.3
Florida 21.1 Louisiana 4.2 Nebraska 7.4

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