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 frequency- 
polygon tends to become very misleading at any part of the 
range, it is better to use the histogram. In the mortality dis- 
tribution of Table IL, for instance, the frequency rises so sharply 
86