336 H. M. POLLOCK, B. MALZBERG AND R. G. FULLER 



from the difficulty of classifying parents in Mendelian language. In order 

 to apply theories of unit characters and determiners, we are compelled to 

 make assumptions with respect to the nature of the mind, in health and in 

 disease, which are in the highest degree improbable. Additional sources 

 of error lie in the difficulty of securing samples that are adequate from the 

 point of view of size and representative character. As a result of his own 

 investigations, Rudin has been able to arrive at merely a negative conclusion 

 to the effect that it has not been demonstrated that Mendelian methods of 

 inheritance do not obtain in certain types of psychoses. This, of course, 

 is a far cry from an affirmative statement that they do. In this preliminary 

 report, therefore, we shall not consider the possibility of Mendelian inheri- 

 tance, but shall turn to the method of mass statistics. Pearson applied 

 this method in 1905, using data reported by Diem in the Archiv fur Rassen 

 und Gesellschaftsbiologie. 3 His reasoning with respect to cancer applies 

 directly to mental disease as well. He wrote as follows: "In dealing from 

 the standpoint of the theory of statistics with the inheritance of any char- 

 acter, say a special form of disease, it is needful to start with a general 

 population, or a random sample of a general population, which has been 

 determined in absolute independence of the presence, or absence of this 

 disease. If we wish to determine the hereditary influence in the case of 

 cancer we must start with a random sample of the general population, or in 

 some manner reconstruct this sample of the general population. We cannot 

 obtain any definite conclusion as to inheritance from the case books of a 

 cancer hospital alone." The last sentence is of particular significance, as 

 only too often has the attempt been made to study the inheritance of mental 

 disease by recourse to case books only. 



The biometric method may be applied as follows: By means of our family 

 histories we are able to count the parents, grandparents, uncles, aunts and 

 siblings and to enumerate the number of psychotic individuals in each group 

 of relatives of the patients. The proportion of affected individuals may 

 then be compared with the corresponding proportion for the general popu- 

 lation. If each class formed a random sample of the general population, 

 the proportion of affected individuals in the class should not differ materially 

 from that of the general population. If, however, the proportion in the 

 general population was significantly greater or smaller, we would reason 

 that the two populations are differentiated from each other; and if the family 

 histories indicated a higher proportion of affected individuals, we would 

 reason, caeterus paribus, that the group under investigation has an inherited 



3 See K. Pearson, On the Inheritance of Insanity, in the British Journal of Medicine, 

 May 27, 1905, page 1175. 



