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 correla- 
efficients, 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 distribu- 
fertility, 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 agri- 
quantitatively 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, fre- 
calculation 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 fluc- 
able 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, 
Tx