VIII IX] 



Accordingly we have 



d/N= -110,7 150 for r=-20 and =-117,1350 for 

 Interpolating linearly for d/N= '114,7679, we find 



Ixxi 



-25. 



The result from the tebrachoric equation is '2317. 



If we use the forward difference formula (e) (p. liii) we find r = '2316, also quite 

 a good result. 



Illustration (x). Ventilation of Home and Health of Mother. 



Health of Mother 



Here 

 while 



We find 



The required value of d/N will be found in the section h= "5 to -6 and k= I'O 

 to I'l in the tables for r = '35, '40 and '45. We therefore first determine d/N for '40. 



z e \ from (a) is given by 



- A ) = '284,788, (1 - a*) = 155,660, 



d/N= '077,2406. 

 h = '56868., k = 1 '01 245, 

 = 6868, < = -3132, % = -1245, ^ = -8755. 



d/N= '080,7857 for r = -40, or from the upper figures. This is too high; we 

 therefore take the value for *35, from the lower figures. These give 



d/N = -075,7559. 

 Hence by linear interpolation 



The exact value is r = '3653. 



:.OL>!S 



