Effect of Precinct-size Variation on Audits corrected

From: Kathy Dopp <kathy_dot_dopp_at_gmail_dot_com>
Date: Fri Aug 18 2006 - 21:54:17 CDT

Re. Calculating Corrrect Audit Sizes

I messed up one variable on one line of my audit calculation algorithm
by dividing by a variable that should not have been there at all (it
was a careless error), and it caused all my precinct-size adjustments
to be HUGELY off. I should have noticed it before by doublechecking
the calcs using excel, but I was busy and assumed that all my program
lines were correct (It seemed like such an easy algorithm to correct
for precinct-size variation & it was, but I screwed up one
expression).

I've recalculated using the Tarrant County precinct data that Jerry
Lobdill provided and have, correctly this time, done a comparison
between not adjusting vs. adjusting for precinct size variation when
auditing precinct optical scan counts, and it makes a big difference
in the probabilities. i.e. for Tarrant County, the probability of
detecting one or more vote miscounts when outcome-altering vote
miscount is targeted to the largest precincts, goes down from the 95%
desired to as low as 45% with some candidate race margins. So
calculating the exact number of precincts that could wrongfully swing
an election, using the total number of ballots cast in any precinct in
which the race was voted on, is critical to maintaining a high
probability of detecting outcome altering vote miscount.

I've attached a small one page pdf with the comparison.

Hopefully, Daniel will be able to finish our web-based program so we
can publicly release our work next week. Frank has the matlab program
and I've asked a friend of mine, Clay, to write a program for the PC
for it as well.

-- 
----
Kathy Dopp
http://electionarchive.org
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Received on Thu Aug 31 23:17:08 2006

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