42 



EMPIRICAL STUDIES OF MEASUREMENT 



Measurements should be on the finest scale that can be recorded 

 without special difficulty. The attenuation by chance error is thus 

 diminished and the time taken in making a more elaborate corre- 

 lation table can be saved ten times over by the use of the Median 

 Ratio. 



The central tendency from which one measures deviations should 

 be chosen with care so that it stands for some reality divergence 

 from which is significant. 



In the relationship given in Table XVII., 1 for instance, from 

 what point should one reckon deviations? The authors take the 

 mean, 56.568. But there is much to be said for taking the modal 

 adult life (at about 70), since that represents an important real 

 tendency and the force of heredity in determining departures from 

 that tenctency is perhaps more important than its form in deter- 

 mining departures fromthe rather arbitrary age, 56.5^8. The re- 



TABLE XVII. 



23 28 33 38 43 48 53 58 63 



73 78 83 88 93 98 



Totals 



of 

 Arrays 



Medians 



of 49 43 47 51 52 55 57 59 62 65 67 68 65 73 74 76 

 Arrays 



Pearson Coefficient = .2853, C.T. being 56.568. 

 Median Ratio = .479, C.T. being 59.4. 



1 The relationship between brother and brother in length of life in cases where 

 both brothers are 21 or over, from ' The Inheritance of the Duration of Life ' by 

 M. Beeton and K. Pearson, Biometrika, Vol. I., p. 84. I have divided the array 

 of 58 so as to make a median sectioning of the series. In the original the array 

 for 58 is given simply as 14, 7, 12, 6, 8, 15, 10, 12, 11, 21, 8, 19, 11, 3, 2. I 

 have also added approximate medians of arrays. 



