Egon S. Pearson 
47 
continuous lines through the points representing the " best " fitting straight lines 
for the 50 observations of Group 1 ; the slopes of these last lines, or constants pb^ 
have been calculated by the Least Square method as in Problem 2, p. 41, and their 
values are given in the 3rd column of Table IV. 
Another way of examining the sessional change, and of obtaining a typical 
representation of it, is to calculate the average values' for the 20 series of yt the 
ith observation in a series ; thus 
m „/ m 
m m 
where pd stands for the mean of the pih. series (63 observations) as opposed to pdi-, 
the mean of a particular Group k of that series. 
The values of Yt represent the sessional variation in any series about the 
mean of that series or session of observations, and the sequence yt — D, t — 1, 
2, 3, . . . 63, will clearly represent the mean sessional change. The values of t/j are 
given at the end of Table II and have been plotted in Figure 4, where they have 
been fitted with the second order parabola (calculated by least squares) 
y = 480 + -00255^ - -0000189^^ (xxx). 
ORDER OF OBSERVATION IN INDIVIDUAL SERIES 
S 2-35 
I I I II M I I I I I I I I I I I I I I m-rm i i i i i i i i i i i ii i i 
60 63 
J-l I M I I I ITTT 
TRISECTION EXPERIMENT, mean sessional change. 
Fig. 4. 
