x.] DISEASE. 167 



bide their time ; they are insufficient for the period in 

 question. By attempting to work with incompleted life 

 histories the risk of serious error is incurred. 



Data. — The Schedule in Appendix G, which is illus- 

 trated in more detail by Tables A and B that follow it, 

 shows the amount of information that I had hoped to 

 obtain from those who were in a position to furnish 

 complete returns. It relates to the "Subject" of the 

 pedigree and to each of his 14 direct ancestors, up to the 

 great-grandparents inclusive, making in all 15 persons. 

 Also, to the Fraternities of which each of these 15 per- 

 sons was a member. Reckoning the total average 

 number of persons in each fraternity at 5, which is 

 under the mark for my R.F.F collection, questions 

 were thus asked concerning an average of 75 different 

 persons in each family. The total number of the 

 Records that I am able to use, is about 160; so the 

 aggregate of the returns of disease ought to have been 

 about twelve thousand, and should have included the 

 causes of death of perhaps 6,000 of them. As a matter of 

 fact, I have only about one-third of the latter number. 



Trustworthiness of R.F.F. data. — The first object was 

 to ascertain the trustworthiness of the medical informa- 

 tion sent to me. There is usually much disinclination 

 among families to allude to the serious diseases that 

 they fear to inherit, and it was necessary to learn whether 

 this tendency towards suppression notably vitiated the 

 returns. The test applied was both simple and just. 



