fractional parts are the middle (giving the median), the outside
quarters (giving the upper and lower quartiles), and similarly the
upper and lower octiles or deciles. This is sufficient for most
purposes. It leaves only the outer eighths or tenths of the cases
undescribed and undetermined, except so far as may be guessed by,
the run of the intermediate portion of the curve, and it defines all
of the intermediate portion with as close an, approximation as is
needed for ordinary or statistical purposes.

Thus the heights of all but the outer tenths of the whole body of
adult males of the English professional classes may be derived from
the five following ordinates, measured in inches, of which the outer
pair are deciles:--

67.2; 67.5; 68.8; 70.3; 71.4.

Many other instances will be found in the Report of the
Anthropometric Committee of the British Association in 1881,
pp. 245-257.

When we desire to compare any two large statistical groups, we may
compare median with median, quartiles with quartiles, and octiles
with octiles; or we may proceed on the method to be described in the
next paragraph but one.

We are often called upon to define the position of an individual in
his own series, in which case it is most conformable to usage to
give his centesimal grade--that is, his place on the base line
AB--supposing it to be graduated from 0° to 100°. In reckoning this,
a confusion ought to be avoided between "graduation" and "rank,"