following results:

---------------------------------------
London | 1.5
Other urban districts | 2.
Rural districts | 2.25
Middle class and Landed Gentry | 3.5
Aristocracy | 4.5
---------------------------------------

In order to apply this formula to the American population I counted
the names in the New York Marriage License Record previous to
1784,[25] and found the number to be 20,396, representing 10,198
marriages. The fifty commonest names embraced nearly 15 per cent of
the whole (1526), or three per cent less than the number found by
Darwin.[26] Of these, one in every 53 was a Smith, one in 192 a
Lawrence, and so on. The sum of the fraction 1/53^2, 1/192^2,
etc., I found to be .000757 or .757 per thousand, showing that the
probability of a chance marriage between persons of the same name was
even less than in England, where Mr. Darwin considered it almost a
negligible quantity.

[Footnote 25: _Names of Persons for whom Marriage Licenses were issued
by the Secretary of the Province of New York_.]

[Footnote 26: _Cf. supra_, p. 21.]

Of these 10,198 marriages, 211, or 2.07 per cent were between persons
bearing the same surname. Applying Darwin's formula we would have 5.9
as the percentage of first cousin marriages in colonial New York.