A. Ritchie-Scott 
113 
N 
r (^11 + - 1) %i + ^11^^21 + 
• + ^n»h2 + 0 • ^*22 + 0 • %2 
+ .4iini3+ 0 . + 0 . ) 
(^21 + - 1) nil + (^21 + ^21 - 1) "21 + 521«3ll 
H- ^21^12 + ^21»^22 + 0 • %2 
+ y42i%3+ ^21»^23 + 0 • %3 
- ^^11 + -Bii - J. - ^ y ^^21 1 -21 - ^ 
«^31 
In the above the P's are ^i^'s and remembering that 
we have 
31 
N 
7\7-2 {d-^ll(i^2l'^*H cPlldP2l '^2l + c^ll c^21 ^''Sl 
iV2 
"t" 116-f*21 (*'^12 + '''is) ~ aPllbPll (*^22 + ''23) + aPllaPzi ("32 + ^33)} 
(89). 
The relation between the coefficients in the above expression is very simple. 
We have already seen that 
N'xW = « (- aP)' + b {,PY + c {,PY + d (- ,Pf (90). 
In the quadrants of a tetrachoric table write the P coefficients. Thus 
-aP +rP 
+ l,p 
The a frequency is related to — ,;P, etc. 
Consider now the empty scheme of an enneachoric table regarded as a tetrachoric 
table with the point of division first at, say, 11 and second at 12, and write in the P 
coefficients as above. 
Biometrika xn 8 
