PSYCHOLOGY: /. A. HARRIS 
67 
personal equation and steadiness of judgment may be determined from 
these data. 
The problems here taken under consideration fall, therefore, into two 
groups. First, those having to do with the existence of personal equa- 
tion in the estimation of the number of objects in samples and of differ- 
ences in personal equation and steadiness of judgment from individual 
to individual. Second, the influence of previous experience upon 
personal equation and steadiness of judgment. 
In the case of all three observers there is a slight but significant 
personal equation, which, notwithstanding the constant effort to im- 
prove, persisted throughout the two years during which the experi- 
ments were intermittently made. In only three out of the twenty-eight 
experiments did the observer lay out samples of too small average size. In 
a large number of the individual experiments the personal equation is 
certainly statistically significant (trustworthy) in comparison with its 
probable error. 
From the experimental data taken as a whole one cannot conclude 
that there is any demonstrated difference between the personal equation 
of the three observers, although the figures do suggest that the bias of 
observer D may be slightly greater than that of either of the others. 
All have a bias in the direction of laying out more than the intended 
number of seeds, but that one is worse than another cannot be asserted. 
In a high proportion of the individual experiments the differences 
between the personal equations of the three observers are statistically 
significant in relation to their probable errors. This is true in cases in 
which (for example) B has a greater personal equation than C, as well as 
in these in which she has a smaller personal equation. 
The probable explanation of this result seems to be that the observers 
vary somewhat in their personal equation from experiment to experi- 
ment, just as they vary from time to time in general health, physio- 
logical tone, and mental vigor, alertness, or whatever one may care to 
call it. As a result of this variation from time to time one observer 
may show an abnormally high personal equation in a particular experi- 
ment in which a second observer shows an unusually low one. On 
another occasion the condition may be exactly reversed. 
Thus in an individual experiment one observer may seem to be de- 
cidedly better than another. In the long run there is no fully demon- 
strated difference between them. 
For steadiness of judgment there is no absolute standard comparable 
with the zero mean deviation of the personal equation. The data show 
a coefficient of variation of about 6.9% in the case of Observer B and C, 
