A. Ritchie-Scott 
95 
regarded in what follows as the leading quadrant and its frequency denoted by m. 
Thus the quadrant shown will have the frequency m^.^ . 
Jn the ordinary scheme for a tetrachoric table, the quadrants are denoted by 
a, h, c, d, and when necessary these letters will be used with the appropriate suffix. 
Thus the division at the point s . f would be represented as in the diagram, 
St 
m . t 
! 
dst 
m . t ' 
N 
The marginal totals corresponding to the leading quadrant are denoted by 
m^., m.t and the complementary totals by m^',, m.t'. 
Clearly any cell frequency may be expressed in terms of quadrant frequencies 
since 
§ 3. 
''^-IJ * ~ "''oJ £-1 + "''s--l> £-!• 
Enneachoric Method. 
In order to determine r, since we assume the distribution to ha normal and we 
know the marginal totals, only one more datum is re(|uired. Tliis for example 
may be a frequency block (or the total frequency on a continuous system of cells). 
As special cases we have the " briquette " or frequency on a rectangle of cells or 
again the quadrant frequency. The block may be the frequency contents of a 
group of corner, marginal or internal cells*. Consider (for future use) the general 
case of a quadrant frequency. 
where and fd are the tetrachoric coefficients. Then 
N 
+ sTi A'" + sr-. A'" + 
= .T„,^o+ ®(.,T, td, r) (1). 
In using Everitt's Tables of the tetrachoric functions in which t„ and 9q must 
be less than | we must either rearrange the table or adjust the above formula for 
the position of the mean with regard to the quadrants. It is more convenient to 
adjust the formula as follows, dropping the suffixes as we are dealing with any point 
of division. 
* A "cell" is the least element for which the frequency is provided in tho original data. Cells grouped 
together for any working purposes are collectively termed a " block." 
