: THEORY OF STATISTICS.
TABLE showing the Greater Fraction of the Area of a Normal Curve to One
Side of an Ordinate of Abscissa ja. (For references to more extended
tables, see list on pp. 857-8.)
Greater Greater
zlo. Fraction of r/o. Traction of
Arca. Area.
0 50000 2-1 "98214
0-1 53983 2-2 ‘98610
0-2 57926 | 2:3 98928
0-3 61791 24 99180
0-4 ‘65542 245 *99379
95 69146 So 99534
06 *72575 A. 99653
0-7 "75804 ew 3 99744
0-8 "78814 29 99813
09 '81594 30 99865
1-0 "84134 Ee] 99903
1:1 86433 2 99931
1:2 *88493 “3 99952
1:3 90320 ot4 99966
14 91924 Lo) 99977
15. ‘93319 2:5 | 99984
1:6 94520 57 99989
17 95543 38 199993
1-8 "96407 39 299995
114) ‘97128 4:0 £99997
2:0 "97725 4-1 99998
17. If we try to determine the quartile deviation in terms of
the standard-deviation from the table, we see that it lies between
0:6 and 070. Interpolating, it is given approximately by
2425 |
{0640 1559 po=0 6750.
More exact interpolation gives the value 0°674489750. This result,
again, is the foundation of the rough rule that the semi-interquartile
 range is usually some 2/3 of the standard-deviation : it is
strictly true for the normal curve only. It may be noted that
the constant 067448975 . . . . can be determined by processes of
interpolation only, and cannot be expressed exactly, like the
mean deviation, in terms of any other known constant, such
as .
It has become customary to use 0:674 . . . . times the standard
error rather than the standard error itself as a measure of the

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