: 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-inter- 
quartile 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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