The risks of errors and covert manipulation are inherent to the use of computer software. Human nature being what it is, those risks are ever-present in all systems that process high-value transactions - especially those involving money or voting. So to achieve trustworthiness, independent auditing of an electronic vote count via of an independent should always be performed.
Both the accuracy and integrity of any paper ballot record must also be assured.
To ensure integrity, no one must be able to alter, delete, or substitute paper ballot records after they are verified by the voter and until they are tallied. Immediately after the election, traditional paper-based audit and control concerns take precedence. In general, the more time passes since creation and the further it travels from point of origin, the more risk there is of manipulation or destruction of paper records.
Unfortunately, there is no such thing as perfect security; the best we can do is to mitigate the risks as best we can. In recognition of this inherent problem, the Canadian system of counting paper ballots in-precinct on election night - in concert with their absentee/early voting procedure - is highly secure. The paper flow is always under observation, and ballots are immediately counted in front of multiple adversarial counterparties - namely the political party representatives.
Admittedly, even rigorous paper-handling processes are not perfectly secure - but on the other hand, in the last 600 years of general use of paper records, we have figured out some pretty good procedures. Yet I doubt that many jurisdictions in America handle paper election records with the level of custodial care that we find, say, in handling real estate collateral in the mortgage-backed securities market, much less in Canadian elections.
There are additional practical problems with checking the trustworthiness of an electronic vote tally after the fact. Since paper ballot records are typically not recounted unless margins are very close, brazen theft would be rewarded in practice. No candidate losing by a large margin wants to challenge an election and force a recount. Political culture being what it is in America, such candidates quickly get labeled as "sore losers" who "waste the public's money and the government's time" on pointless recounts, and who use "conspiracy theories" to compensate for their inability to admit they lost.
Although New Hampshire’s experience with recounts appears to show that electronic and paper tallies seldom differ by a significant number of votes, relatively few “top ticket” races have been recounted - presumably the rewards of altering the outcome of major state or federal offices are more likely to outweigh the risk of discovery.
When statewide recounts of paper ballot records for high-stakes races occur, recent experiences in Ohio and Washington state clearly reveal the potential for flaws in both approach and execution in conventional recount and spot audit protocols.
I personally believe that New Hampshire is better served by enhancing its hand-counted paper ballot protocols, to retain full citizen control and oversight of the electoral process. On the other hand, as long as optical scan tabulation is performed, counting some of the ballots by hand and comparing to the electronic tally can identify accidental or deliberate mistabulation of the vote. The details of the independent hand count protocol determine the probability of detection.
There are two general approaches for hand count validation of electronic vote tabulation: precinct random spot audits and universal ballot sampling. Several states currently rely on precinct random spot audits; for example, California counts 1% of its precincts by hand, and Minnesota performs a random post-election hand-count audit of 2 precincts per county (amounting to somewhat more than 4% of the total number of precincts). Due to differences between the human and the electronic and mechanical interpretation of voter intent, small discrepancies are not necessarily a sign of systematic mistabulation - although there are credible exploits in close elections where outcome-altering results can be determined by just a few votes per precinct. Typically there is a formal or informal standard for expanding the hand-count validation if significant discrepancies are detected; in Minnesota the standard for expanding the audit is a 0.5% discrepancy between the hand and machine tally.
There are several potential drawbacks with conventional precinct spot-audit protocols. (1) There are classic concerns about chain of custody which are proportional to the time which passes between casting the ballot and performing the hand count validation. Ideally, the spot audit would occur in precinct on election night. (2) The recent conviction and sentencing of election officials in Ohio who “gamed” the selection of precincts for the Ohio partial recount to ensure that no discrepancies would be detected illustrates the difficulty of ensuring true random selection is followed. (3) If hand count validation occurs in only a few percent of precincts and mistabulation is clustered, the laws of statistics tell us that there can still remain a significant chance that the mistabulation is not detected. (4) Clustered mistabulation may be detected, but the magnitude of the discrepancy may be too small to expand the audit further. Political pressures may be placed on a candidate such that even if a suspicious pattern of discrepancies is detected - but it appears to be insufficient to change the outcome - it would not be practical to continue to contest the result and expand the audit. (Candidates do not wish to be labeled a “sore loser”.)
The Election Defense Alliance has created and published the results of computer simulations of a variety of precinct spot-audit protocols - such as the ones proposed in Washington DC in 2006 as HR 550, and this year, as HR 811. Our findings indicate that especially in the case of the US House of Representatives (involving on average about 440 precincts, nationwide), there is an unacceptably high rate of failure to detect outcome altering mistabulation in many credible scenarios as modeled.
The alternative hand-count election verification protocol involves a somewhat counter-intuitive approach: hand-counting a few percent of the vote in 100% of the precincts, rather than hand-counting 100% of the vote in a few percent of the precincts.
This protocol - which Election Defense Alliance calls UBS, or “Universal Ballot Sampling” - randomly selects a sample of individual ballots from every precinct voting location, and hand-counts just those ballots. The rationale for doing so is that this is an analogy to a “public opinion poll”, in that it randomly samples ballots for hand-counting in much the same way that an opinion poll randomly samples a population. If enough ballots are sampled and hand-counted, the accuracy of that sample can be estimated to a high degree of precision - just as the margin of error of a random public opinion poll can be estimated to a high of precision. It turns out that randomly sampling approximately 15,000 - 20,000 votes in any contest should produce a sample that reflects the outcome of the election as a whole within plus or minus 1%, with 99% certainty.
Since most US House races generate 150,000 - 200,000 votes, simply randomly sampling every tenth ballot in a precinct should ensure that when the precinct hand count sample results are rolled up, the votes for US House candidates in the sample match the votes in the electorate as a whole within plus or minus 1% with high confidence.
Election Defense Alliance has created computer simulations of the UBS protocol and empirically verified that, if the precinct ballot sample is random, indeed UBD did detect 100% of simulated mistabulations > 1% of the vote.
This addresses several problems with the alternative, precinct spot-audit approach. If the UBS and the optical scan tally are within 1% with the sample sizes indicated, there should be high confidence that there was no significant machine mistabulation. The false-positive rate should be very low.
On the other hand, if the difference between the UBS result and the optical scan tally is greater than 1%, there is a strong and objective mathematical case for a candidate to challenge the official tally and request an expanded hand (re)count. Since the UBS results are available as soon as the optical scan tally is available, a candidate is also empowered to challenge suspect results before the “official” tally becomes fixed in the minds of the voting public and their political peers.