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Chapter 1: Introduction and Graphical Displays
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Observe that the distribution has a longer tail to the left, with more of the
values to the left of the peak. If this were a truly representative sample from
the population, then one would expect that the distribution of the population
of dollars spent by the students would have a similar shape. Also, observe
that the polygon is “tied down” to the horizontal axis at both ends. The
points where the polygon is tied down correspond to the midpoints of the
classes with zero frequency.
Note:
Midpoints of classes are also called class marks or class midpoints.
Sometimes, the frequency polygon and the relative frequency polygon can
be superimposed onto the histogram for the same data.
Figures 1-20
show
the frequency and relative frequency polygons superimposed on the
histograms for the data in
Example 1-3
. These can be generated from the
Frequency and Relative Frequency Superimposed on Histogram
workbook.
Click here for the Frequency Polygon and Relative Frequency Polygon Workbook