Re: Voting System Standards

From: Douglas W_dot_ Jones <jones_at_cs_dot_uiowa_dot_edu>
Date: Sun Jul 27 2003 - 18:47:48 CDT

The paper ballot represents the authentic vote in this system. But the
electronic record is valuable for two main reasons:

1) Faciltates tabulation of the vote
2) Serves as additional security against several forms of attack (for
example, ballot box stuffing, counterfeit ballots, swapping ballots,
destroying ballots, rigged scanners).

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The electronic record could be used to give a very quick but accurate
election result. Once the files are transferred from the precinct to the
county headquarters, tabulation should take seconds. But this will be the
preliminary unofficial unaudited tally. We can get a very good idea of the
winners by sampling the paper ballots.

We can use binomial distribution to do the calculations. I have a
calculator that a fellow by the name of Bill Buck helped me with. It's in
Excel and uses the BINOMDIST function in Excel. I am trying to get someone
else to write a standalone calculator. Anyway, if you have Excel you can
try it out here:

In this case, the sample is accepted if no defects are found -- rejected if
one is found. So, the "defects found in sample" will have to be zero.

For example, suppose in a two way race candidate A got 505,000 votes and
candidate B got 495,000 according to the electronic record. Let's say, for
now, that if we compute a 99.999 percent confidence level, we can safely
announce candidate A as the winner (with 99.999, we'll be wrong once in
100,000 contests). The outcome could only be wrong if 5,000 votes turn out
to be taken away from A or added to B. This is a fraction of .005 of the
million votes cast. If we enter .005 in the LOT FRACTION DEFECTIVE cell
along with 1,000,000 in the "Election Size" field and play with the required
sample size, we can find a number that will give us the 99.999 Confidence
Level we want. A few tries and I get .99999 with 2,300 samples. So with
this in mind, we know if we can collect a random sample of 2,300 ballots and
check them against the electronic record (and the match), we are 99.999
percent certain that Candidate A won. This sample could be obtained pretty
quickly. A fuller audit can be performed later. In practice, samples will
usually be much smaller since races are usually won or lost by several
percent -- not so close as this example. For example, you only need a
sample of 550 ballots where a 2.5 percent swing could change the outcome.

If everyone follows procedures, there should not be any mismatches. Even if
a defect is found (for example, a paper ballot that has no corresponding
record in the electronic table of ballot images), it won't necessarily
disturb the outcome -- it will just take a little longer. You just take a
larger sample until you reach the desired confidence level. If more than a
few defects are showing up, we may have to scan all the ballots. Again,
this might delay the result slightly but still should be done fairly
quickly. We can then also do hand sampling of the scanned result for
further verification.

It may be that all the ballots will be scanned as the election is audited in
the days after Election Day.
more on this later.

Received on Sun, 27 Jul 2003 16:47:48 -0700

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