Januabt 24, 1913] 



SCIENCE 



137 



taken as a symptom with his status in other 

 traits of whose condition it may be a symp- 

 tom is of course of wider application than 

 shown in the ease supposed. An individ- 

 ual's status in anything may be thus com- 

 pared with his status in anything else and 

 the correspondence measured. Achieve- 

 ment in school studies may be compared 

 with achievement in adult life ; how far 

 skill in motor control and craftsmanship is 

 a sjonptom of ability in abstract intellec- 

 tual operations may be determined; 

 whether mental ability is or is not indica- 

 tive of mental health may be decided ; what 

 an individual's interests mean for his ca- 

 pacities, or what his ability in any one test 

 means concerning his ability in any other, 

 may be found out. 



One special application of the method of 

 correlation is so important as to deserve 

 separate mention. This is its use in test- 

 ing a symptom by its correlation with some 

 future condition. When a psychological 

 or educational measurement of an individ- 

 ual enables us to make a successful proph- 

 ecy concerning the individual's future and 

 one that could not otherwise have been 

 made, we have not only the most impressive 

 but also the soundest proof of the signifi- 

 cance of the symptom in question. Thus 

 we rightly increase our faith in Mr. 

 Courtis's analytic tests of arithmetical 

 abilities, if we find that he is able to 

 prophesy truly that a certain student's 

 work in algebra will be greatly improved 

 by certain specified drills in the funda- 

 mental operations in arithmetic, though the 

 usual observations of her teachers gave no 

 hint of this. 



The most important accomplishment of 

 the last decade's study of intellectual and 

 moral diagnosis has been to establish prin- 

 ciples of method for testing symptoms. But 

 there has been also a substantial beginning 



in accumulating facts of symptomatology 

 which education and the other social arts 

 can henceforth use. These I shall not try 

 to summarize, but only to illustrate. 



As our first illustration of the knowledge 

 of intellectual diagnosis that has been at- 

 tained and may be expected soon to be 

 much increased, let us take the case of gen- 

 eral intellect — the ability to manage ideas 

 — the average station of a man in respect 

 to that group of powers which we call in- 

 tellectual. 



In order to avoid technicalities and to 

 gain clearness I shall go somewhat beyond 

 the specific results obtained by Burt, 

 Bonser, Norsworthy, Simpson, Spearman, 

 Krueger, Peterson and myself in testing 

 tests of general intellectual ability. I shall 

 in fact be guilty of prophesying what would 

 occur rather than measuring what has 

 actually been found to occur. However, 

 the prophecy follows by straightforward 

 inferences from facts found by one or 

 another of these workers. Moreover, since 

 I shall be careful to underestimate rather 

 than overestimate the closeness of the cor- 

 relation between an individual's general in- 

 tellectual ability and his ability in any of 

 the tests, the prophecy will be safe as an 

 argument that the results of the study of 

 mental tests are beginning to be impoi-tant 

 for education and the other arts of social 

 control of human nature. 



Suppose the men and women of this audi- 

 ence were measured in respect to these eight 

 tests, four trials of each being given : 



1. Supplying words to make sense in mutilated 

 passages, the four trials being of four grades of 

 difficulty. 



2. Giving the opposites of words, each trial com- 

 prising twenty words, the four trials being of four 

 grades of difficulty. 



3. Memorizing a given word in connection with 

 a given form, as in Fig. 1, so as to give the former 

 when the latter is presented (there being ten pairs 

 in each "trial"). 



