1: THEORY OF STATISTICS. 
may be readily obtained from such a curve by dividing the 
terminal ordinate into ten equal parts, and projecting the points 
So obtained horizontally across to the curve and then vertically 
down to the base. The construction is indicated on the figure for 
the fourth decile, the value of which is approximately 2-88 per cent. 
29. The curve of fig. 26 may be drawn in a different way by 
taking a horizontal base divided into ten or a hundred equal 
parts (grades, as Sir Francis Galton has termed them), and erecting 
at each point so obtained a vertical proportional to the cor- 
responding percentile. This gives the curve of fig. 27, which was 
obtained by merely redrafting fig. 26. The curve is of so-called 
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Grades 
Fic. 27.—The curve of Fig. 26 redrawn so as to give the Pauperism 
corresponding to each grade: Galton’s ‘‘ Ogive.” 
ogive form. The ogive curve for the distribution of statures 
(Example iii.) is shown for comparison in fig. 28. It will be noticed 
that the ogive curve does not bring out the asymmetry of the 
distribution of pauperism nearly so clearly as the frequency- 
polygon, fig. 10, p. 92. 
30. The method of percentiles has some advantages as a method 
of representation, as the meaning of the various percentiles is so 
simple and readily understood. An extension of the method to 
the treatment of non-measurable characters has also become of 
some importance. For example, the capacity of the different boys 
in a class as regards some school subject cannot be directly 
measured, but it may not be very difficult for the master to 
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