Tablet fa- Stutixtii-iaiix <tn</ /iiiinntri<-i<tn* [XX IX 



TAIU.K \.\I.\ (pp. 4251) 



Tables of the Tetraclmric functions. (P. F. Kvcritt, llinmvtnfoi. Vol. vn. 

 pp. 437451.) 



The purpose of these tables is to expedite the calculation of tetrachoric /,, the 

 correlation coefficient from a four-fold table, when we suppose the variates to be 

 Gaussian in the law of their frequency. 



Let the table be 



where o is the quadrant in which the mean falls, then b + d and 

 each less than N. Let 



then 



are clearly 



T,,T rl '/-" + ............ (xxxvii) 



is the equation to determine r the tetrachoric correlation, and Table XXIX gives 

 the values for given T O , Le. ^ (1 a) of the following six tetrachoric functions 

 TI, T.J ... T,, and further of h, the ratio of the abscissa of the dichotomic line to tin- 

 standard deviation of the corresponding variate. 



It is occasionally needful to go beyond the first six tetrachoric functions. In 

 this case the following finite difference formula is available : 



where 



(xxxviii), 



(- 2). \'n (H - 1 ) .................. (xxxix). 



The following table gives the values of p n and */ from n = 7 to 24. 



