X.—CORRELATION: ILLUSTRATIONS AND METHOD. 209 
Roy. Stat. Soc., vol. xlvii,, 1884, p. 34. (This paper was written 
before the invention of the correlation coefficient, but is cited because 
the method of Illustration v. is used to separate the periodic from the 
secular movement: see especially § ix. on the process of averaging 
employed.) 
Theory of Correlation in the case of Non-linear Regression, 
and Curve or Line fitting generally. 
(17) PEARSON, KARL, “On the Systematic Fitting of Curves to Observations 
and Measurements,” Biometriko, vol. i. p. 265, and vol. ii. p. 1, 1902, 
(The second part is useful for the fitting of curves in cases of non-linear 
regression. ) 
(18) Pearson, Karyn, On the @Qeneral Theory of Skew Correlation and Non- 
linear Regression, ‘‘ Drapers’ Co. Research Memoirs : Biometric Series,” 
11. ; Dulau & Co., London, 1905. (The ‘f correlation ratio.”) 
(19) Pearson, KARL, “ On a Correction to be made to the Correlation Ratio,” 
Biometrika, vol. viii., 1911, p. 254. 
(20) PearsoN, KArL, “On Lines and Planes of Closest Fit to Systems of 
Points in Space,” Phil. Mag., 6th Series, vol. ii., 1901, p. 559, 
(21) Pearson, Karn, “On a General Theory of the Method of False 
Position,” Phil. Mag., June 1903. “(A method of curve fitting by 
the use of trial solutions.) 
(22) BLAKEMAN, J., “On Tests for Linearity of Regression in Frequency- 
distributions,” Biometrika, vol. iv., 1905, p. 332. 
(23) Snow, E. C., “On Restricted Lines and Planes of Closest Fit to Systems 
of Points in any number of Dimensions,” Phil. Mag., 6th Series, vol. 
xxi., 1911, p. 567. 
(24) SvuTsky, E., “On the Criterion of Goodness of Fit of the Regression 
Lines and the best Method of Fitting them to the Data,” Jour. Roy. 
Stat. Soc., vol. Ixxvii., 1913, pp. 78-84. 
Abbreviated Methods of Calculation. 
See also references to Chapter XVI. 
(25) Harris, J. AkTHUR, ‘‘ A Short Method of Calculating the Coefficient 
of Correlation in the case of Integral Variates,” Biometrika, vol. vii., 
1909, p. 214. (Notan approximation, but a true short method.) 
(26) HARRIS, J. ARTHUR, ‘‘On the Calculation of Intra-class and Inter-class 
Coefficients of Correlation from Class-moments when the Number of 
possible Combinations is large,” Biometrika, vol. ix., 1914, pp. 
446-472. 
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