THEORY OF STATISTICS.
interval is not the same, as suggested by the histogram. The
area shown by the frequency-polygon over any interval with an
ordinate y, (fig. 3) is only correct if the tops of the three
successive ordinates v;, 7, 7; lie on a line, s.e. if Yo=3(y, +95),
the areas of the two little triangles shaded in the figure being
cqual. If y, fall short of this value, the area shown by the
Fie. 4.
polygon is too great; if y, exceed it, the area shown by the
polygon is too small; and if, for this reason, the frequencypolygon
 tends to become very misleading at any part of the
range, it is better to use the histogram. In the mortality distribution
 of Table IL, for instance, the frequency rises so sharply

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