4135 THEORY OF STATISTICS.
Pearl, Raymond, normal distribu- for unmeasured characters, 152-tion
 of number of seeds in Nelum- 153, refs., 333; standard errors
bium, 306. Refs., probable errors, of, 337-341 ; correlation between
355 ; errors in variety tests, 396 ; errors of sampling in, 341-342;
Introduction to Medical Biometry, refs., 154.
397. Perozzo, L., ref., applications of
Pearson, E. S., refs., polychoric co- theory of probability to correlaefficients,
 390; probable errors, tion of ages at marriage, 314.
395. Persons,  W. M., refs, index-Pearson,
 Karl, contingency, 63, 65 ; numbers, 390.
mode, 120; standard-deviation, Petals of Ranunculus bulbosus, fre-144
 ; coefficient of variation, 149 ; quency of, 102; unsuitability of
skewness, 149; inheritance of median in case of such a distribufertility,
 195; spurious correla- tion, 117.
tion between indices, 215; bi- Peters, J., refs., multiplication table,
nomial apparatus, 299 ; deduction 358.
of normal curve, 306; data cited Petty, Sir W., refs., Economic
from, 70, 78, 90, 96, 122, 160, 161. Writings, 6.
Refs., correlation of characters not Pickering, S. U., refs., errors of agriquantitatively
 measurable, 40, cultural experiment, 396.
333; contingency, etec., 72-73, Poincaré, H., refs., Calcul des prob-333,
 390, 395; frequency-curves, abilités, 361.
105, 130, 154, 273, 289, 314, 315, Poisson, S. D., law of small chances,
354, 393; binomial distribution 368, 369; refs., sex-ratio, 273 ;
and machine, 314; hypergeo- Recherches sur la probabilité des
metrical series, 289 ; dissection of Jugements, 273, 361.
compound normal curve, 315; Poppies, stigmatic rays on, frecalculation
 of moments, 225; quency, 78; unsuitability of
general methods of curve-fitting, median in such a distribution,
209; testing fit of theoretical to 116.
actual distribution, 315, 391, 394; Population, estimation of, between
correlation and correlation-ratio, censuses, 125-126 ; refs., 130, 253.
188, 209, 225, 252, 333, 390, 391, Positive classes and attributes, def.,
392 ; fitting of principal axes and 10; number of positive classes,
planes, 209, 333; correlation be- 13 ; sufficiency of, for tabulation,
tween indices, 226, inheritance of 13; expression of other fre:
fertility, 226; weighted mean, quencies, in terms of, 13-14.
reproductive selection, 226 ; prob- Poynting, J. H., correlation of flucable
 errors, 355, 393, 395; tables tuations, 201 ; refs., 208.
for statisticians, 358; polychoric Precision, 144, 257, 304.
coefficients of correlation, 390; Prices, index-numbers of, 126; use
variate difference method, 392. of geometric mean, 126 ; of har-Peas,
 applications of theory of sam- monic mean, 129 ; refs., 130-131,
pling to experiments in crossing, 390-391.
267-268. Principal axes, in correlation, 321-Pecten,
 correlation between two 322; ref., 333.
diameters of shell, 158 ; constants, Probability, theory of, works on,
(qu. 3) 189. refs., 361, 396-397.
Percentage, standard error of, 256
257 ; when numbers in samples QUARTILE deviation. See Quartiles.
vary, 264-265. See also Sam-  Quartiles, quartile deviation and
pling of attributes. semi-interquartile range, 134;
Percentiles, 150-153 ; def., 150 ; de- generally, 147-149; defs., 147;
termination, 151-152 ; advantages determination, 147-148 ; ratio of
and disadvantages, 152-153 : use q.d. to standard-deviation, 148,

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