[EL] McDonald study, birthdate distribution in real voter list

[Adam Morse]

Isn't the question actually "given a distribution of names and a
distribution of birthdates, what are the odds of a pair of people
duplicating both a birthdate and a name?"  We don't care in advance whether
it's Robert Smith that has a false duplicate or Jane Smith, but we care what
the total frequency of duplications of both name and birthdate is across all
names.  That's not quite the same as the way you're phrasing it.

Also, intuitively this will be sensitive to the total size of the pool and
to the distribution of names within the pool, and the distribution of names
over time, which also won't be the same--Aedan is a much more common name
now than it was 20 years ago, when it was much more common than 40 years
ago.  Changing ethnic distributions will produce similar effects among
surnames.  But leaving aside the change over time, I wonder how much of the
difference between what Bev is seeing and what Michael and Justin calculated
depends on the size of the pool--when you care about the total number of
multiple chance hits, the difference between 600,000 voters and 2.5 million
voters is vastly more than the simple ratio of 4:1.

--Adam Morse

On Sun, Sep 11, 2011 at 2:39 PM, Bev Harris <bev at blackboxvoting.org> wrote:

> Forgive me if I'm wrong, but isn't the question whether a specific person,
> Robert Smith, has the same birthdate as a different Robert Smith? The
> question
> is not whether any two people in a pool share a birthday.
>
> The number of shared birthdays among all people on the list works out to
> about
> 1:10,000 (in a large list), which can readily be seen just by counting the
> shared birthdates on the list. (On a small list, the presence of twins will
> provide an extra sprinkle of same birthdates)
>
> The chances that one specific individual shares the same birthdate as
> another
> specific individual is the question. The rest of the people in the room
> really
> don't matter.
>
> > Put differently, the question isn't whether two people on a list share a
> > single date of birth, but whether _no_ two people in a large pool share
> > a birthday.
>
>
> Bev Harris
> Founder - Black Box Voting
> http://www.blackboxvoting.org
>
> * * * * *
>
> Government is the servant of the people, and not the master of them. The
> people, in delegating authority, do not give their public servants the
> right
> to decide what is good for the people to know and what is not good for them
> to
> know. We insist on remaining informed so that we may retain control over
> the
> instruments of government we have created.
>
> Black Box Voting is a nonpartisan, nonprofit 501c(3) elections watchdog
> group
> funded entirely by citizen donations.
> http://www.blackboxvoting.org/donate.html
> Black Box Voting
> 330 SW 43rd St Suite K
> PMB 547
> Renton WA 98057
>
>
> ----------------------------------------------------------------
> This message was sent using IMP, the Internet Messaging Program.
>
> _______________________________________________
> Law-election mailing list
> Law-election at department-lists.uci.edu
> http://department-lists.uci.edu/mailman/listinfo/law-election
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://webshare.law.ucla.edu/Listservs/law-election/attachments/20110911/c8b1629f/attachment.html>