Jan. 3, 1921 



Correlation and Causation 



569 



and that the variables are connected only by the paths shown above. 

 In a certain stock of guinea pigs the following correlations were found: 



Birth weight with interval, rxp = +0.5547. 



Birth weight with litter, r XL = — 0.6578. 



Interval with litter, r^ = — 0.4444. 



We are able to form three equations of type r x ? = '2p x . x p Y . K an d three 

 of type 2/> 2 x . A + 22/> x . A /> x . B r AB = 1. These six equations will enable us 

 to calculate six unknown quantities. The six path coefficients in the 

 diagram in figure 7 can thus be calculated from the information given 

 here, but no others. 



The equations are as follows: 



From (1) and (2), p x . r = p = o. 3269 



ql=—o. 5125 

 From (4), Px-Q = q = 0.8627 



Pq-l=1 =—0.5941 

 pQ.\ = a = o. 8044 



