THE SCOPE OF PSYCHOLOGICAL TESTS I93 
an actual trial. The psychologist who presumes to apply 
tests to kinds of work which he understands only super 
ficially to groups of men whose work is alike only in 
superficial details, and in cases where the reliability of the 
results rests not upon an impersonal record of actual work 
but upon a concoction of personal opinions, is indeed 
taking a very grave risk of bringing his medium into dis 
repute among those whose business it is to be familiar 
■with the complexities and intricacies of employment work. 
No doubt all of these faults have occurred in the experi 
ments described here; but they are recognized as weak 
nesses and the results discounted accordingly. 
The virtue of the psychological method consists in 
a pplying to the abilities of people certain scientifically 
accurate tests, tests whose value has first been deter 
mined by means of experiments which meet the conditions 
described. The superiority of such measures over the 
ordinary haphazard measures of common sense is ob 
vious. However, this very virtue is also the weakness of 
the psychological method or, in fact, of any scientific 
method. Tests and measures are only significant when 
applied to cases which conform to standard conditions. 
The diagnostic tests applied by the physician, for instance, 
e nable him to determine the nature of an illness like 
measles which, because of its invariable symptoms, we 
may call standard. However, as soon as an extraordinary 
dlness occurs, his tests become useless. They do not 
enable him to diagnose the nature of the disease, and it 
becomes necessary to call in specialists who, in many cases, 
are also unable to determine the exact nature of the 
trouble. The more complicated and exceptional the disease, 
the less applicable are the ordinary laws and measures 
°f the physician. Exactly the same condition prevails in