REACTION-TIME OF GONIONEMUS MURBACHII. 93 



not equal, but when we consider the reaction-times we find that 

 the ratio of variability to reaction-time is in each case 1:4. Al- 

 though the absolute variability is in one case three times as great 

 as in the other, it is 25 per cent, of the average reaction-time in 

 both instances. 



Heretofore I have expressed relative variability as a ratio 

 (M.V. : M.), or as a percentage value of the mean (M.V. = x per 

 cent, of M., in which case x = R.V., the relative variability.) 



Obviously it is always important in comparative reaction-time 

 work to know the relative variability of reactions ; in fact it is 

 often quite impossible to make significant comparisons of results 

 until this value is found. For this reason I have given in every 

 table of this paper the percentage value of the mean variation in 

 terms of the mean. This value I have called the relative vari- 



* 



ability (R. V.). It is obtainable by the formula recently used 

 by Myers, ' v.c. = m.v. x loo/av. In this formula, which as 

 inspection shows gives the ratio (in per cent.) of m.v. to av., v.c. 

 is a value called by Myers the variation-coefficient, and av. is the 

 mean (M.). Supposing a reaction-time of .180 second to have 

 an absolute variability of .020 second, then by the formula 

 (.020 x lOO/.iSo) the variation-coefficient (Myers), or what I 

 prefer to call the relative variability (R. V.), is I i.i + . If we 

 chose this value might be written ii.i -(-per cent., thus indi- 

 cating that the absolute variability (M. V.) is ii.i + P er cent, of 

 the average reaction -time (M.). 



Since Pearson 2 in this statistical work has made use of a quan- 

 tity which he calls the "coefficient of variability," and which is 

 obtained by the formula 



C. V. = - - x 100, 



it seems unwise to use the term variation -coefficient, suggested 

 by Myers, for this new quantity in reaction-time work. As the 

 value which we obtain by Myers' formula is in reality the per- 



1 Myers, Chas. S.: "Reports of the Cambridge Anthropological Expedition to 

 Torres Straits." Vol. II., "Physiology and Psychology," Part II., 1903, p. 212. 



2 Pearson, Karl : " Mathematical Contributions to the Theory of Evolution, III., 

 Regression, Heredity and Panmixia," Phil. Trans. Roy. Soc. London, Vol. 187, A, 

 pp. 253-318. 



