454 



THE SCI EXT IF IC MONTHLY 



ring at each age, has the form of a very much stretched letter S resting 

 on its back. Some years ago Pearson undertook the analysis of this 

 complex curve, and drew certain interesting conclusions as to the 

 fundamental biological causes lying behind its curious sinuosity. His 

 results are shown in Figure 8. 



















PEARSON'S 



GRADUATION 



OF 





d-x 













































































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i 



-+ 



j. 















































































































ji 









































































































































































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/INF 



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* 

























































1 



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•jS* 





N s. 

















i 





ZHiLDHOOC 























..-' 











AGL 



















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youTH^, 





. 







..*''' 

















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''_■ t 



20 <h 



DOLL 



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SO 





"J 







YEARS OF LIFE 



FIG. 8. SHOWING PEARSON'S RESULTS IN FITTING THE Dx LINE OF THE LIFE TABLE 



WITH 5 SKEW FREQUENCY CURVES. Plotted from the data of Pearson's original memoir on 



"Skew Variation" in the Phil. Trans. Roy. Soc. 



He regarded the d x line of the life table as a compound curve, and by 

 suitable mathematical analysis broke it up into five component fre- 

 quency curves. The data which he used were furnished by the d x line 

 of Ogle's life table, based on the experience of 1871 to 1880 in Eng- 

 land. This line gives the deaths per annum of one thousand persons 

 born in the same year. The first component which he separated was 

 the old age mortality. This is shown by the dotted curve having its 

 modal point between 70 and 75 years, at the point lettered O x on the 

 base of the diagram. This component, according to Pearson's gradua- 

 tion, accounted for 484.1 deaths out of the total of 1,000, or nearly 

 one-half of the whole. Its range extends from under 20 years of age 

 to the upper limit of life, at approximately 106 years. The second 

 component includes the deaths of middle life. This is the smooth curve 

 having its modal point between 40 and 45 years at the point on the 

 base marked 2 . Its range extends from about 5 years of age to about 

 65. It accounts for 175.2 deaths out of the total of 1,000. It is a long, 

 much spread out curve, exhibiting great variability. The third com- 

 ponent is made up by the deaths of youth. This accounts for 50.8 

 deaths out of the total of a thousand, and its range extends from about 

 the time of birth to nearly 45 years. Its mid-point is between 20 and 25 

 years, and it exhibits less variability than either the middle life or the 

 old age curves. The fourth component, the modal point of which is at 

 the point on the base of the diagram marked 4 covers the childhood 



