Exit Polls: Is opposition right in blaming EVMs? Why demand for 50% VVPAT check has no ‘statistical basis’

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Updated: May 21, 2019 12:05 PM

Political parties have often questioned EVMs and have alleged they can be tampered with — a charge that has been vehemently denied multiple times by the Election Commission. Do these allegations have any statistical basis?

EVM, VVPAT, Lok Sabha election resultA VVPAT is an auxiliary, independent device linked to an EVM to allow voters to see if the votes cast by them have gone to the right candidate. (File Photo)

Lok Sabha election result 2019: A series of exit poll 2019 results released on Sunday predicted another term for the BJP-led NDA government under Prime Minister Narendra Modi. The saffron party is set to be back in power — if the predictions hold true — possibly with an even bigger majority than in 2014. However, the Opposition made it clear that it is not going to concede defeat so easily. Resorting to its oft-used tactic post the 2014 Lok Sabha election results, some parties have already started questioning the electronic voting machines (EVMs). Dismissing the exit poll results announced last evening, West Bengal CM Mamata Banerjee said ‘the game plan is to manipulate or replace thousands of EVMs through this gossip’. Delhi’s ruling Aam Aadmi Party has gone a step ahead and called for the cancellation of elections in case of any divergence in the EVM and VVPAT count.

Lok Sabha Election 2019: Full Coverage

One gets the sense that this is how opposition parties are likely to react in case results go against them on May 23. The first casualty, unfortunately, will be the Election Commission. In April this year, 21 political parties moved the Supreme Court demanding the audit of at least 50 per cent VVPATs. However, the court concluded after a series of hearings that the electoral process was fair and there was no need to go for 50 per cent testing. It, however, increased the number from one to 5 VVPAT tests on each assembly seat. The opposition filed a review petition which was again dismissed by the top court.

What is the EVM-VVPAT issue all about?

The political parties on many occasions have questioned the security features of voting machines and they believe that the EVMs can be tampered with — a charge that has been vehemently denied multiple times by the EC. But to instill confidence among the voters and political parties, the commission introduced voter-verified paper audit trail (VVPAT) machines that generate a paper slip after a vote has been cast. The voter can see whether vote went to the person or candidate it voted for. The Commission started matching the slips of one machine in one assembly constituency. But some parties claimed that one machine per constituency has very little chance of detecting an error, therefore the paper slips of at least 50 per cent VVPATs should be matched.

Also Read: Reading the tea leaves: Chandrababu Naidu cites risk of EVM manipulation, asks EC to resolve issues

What is the Election Commission’s Stand?

The EC maintained that EVMs are foolproof and it did not find any discrepancies in any of those paper audit machines it matched in the past, ensuring 100 per cent fairness in the poll process. The poll body, however, approached the Indian Statistical Institute (ISI) to find out a reasonable sample size of polling booths where slip verification must be carried out to achieve the objective of establishing the credibility and integrity of the present system. The institute put to use statistical methods and came out with a number that was even lesser than what the poll body used to test.

What Indian Statistical Institute Recommended

The ISI found that if 479 paper audit machines are tested among the total EVMs that have been used for a set of polls — Lok Sabha or Assembly elections for which counting is done at the same time — and if no mismatch reported, it can be concluded that the proportion of defective voting machines is less than two per cent. The ISI states in its findings: “We recommend that a random sample of the Electronic Voting Machines of size 479 be drawn from the population of all the EVMs that have been used in that set of elections. If for each of the selected machines, the EVM count matches with the VVPAT count, then it can be concluded with an extremely high statistical confidence (more than 99.993665752% confidence) that the proportion of defective EVMs is less than 2%.”

The report suggests that 2 per cent or 0.02 margin of error seems appropriate as it is unlikely to affect the final outcome. The ISI says that “in all applications of sampling theory, a reasonable margin of error is necessary as any sample, howsoever randomly chosen, cannot be the exact replica of the population as a whole…In this context of sampling of EVMs, in our view 2% or 0.02 margin of error seems appropriate”.

Also Read: TMC miffed with exit poll predictions; says forecasts baseless, biased towards BJP

The report also states that the EC has already undertaken 1,521 such EVM-VVPAT slip verifications but not a single mismatch of votes has been found in each of these randomly sampled EVMs.

Opposition’s demand for 50% VVPAT match lacks statistical basis

The Financial Express Online reached out to an expert to know whether the opposition parties are right in demanding 50 per cent paper audit. The official, on the condition of anonymity, said that the opposition’s demand for 50 per cent matching of paper slips have ‘no statistical basis’. “This 50 per cent has no statistical basis. Earlier petitions mentioned 20 per cent now they are asking for 50 per cent. How is it good because the other 50 per cent may be tampered with as well. Somewhere they (political parties) are assuming that 50 per cent checking would be good enough. Samples give some idea of the population. They are wrong in assuming that the small sample size is unlikely to give correct results for the large population. That is mathematically not borne out.”

He further said: “If two per cent EVMs are defective then it is almost impossible that a sample of 479 will have zero defect (it will be detected). In the population of 10 lakh or 1 lakh does not matter, if there are two per cent defectives then 479 size is almost certain to catch at least one of the defectives. That is the basis of statistics.” The official also said increasing the number of samples may not increase the confidence and the marginal increase in confidence is not proportionate to increase in the resource required.

Supreme Court order on EVMs-VVPAT

The Supreme Court has asked the EC to increase the verification of VVPAT from 1 to 5 per assembly segments in a parliamentary constituency. The SC in its order writes: “At the very outset the Court would like to observe that neither the satisfaction of the Election Commission nor the system in vogue today, as stated above, is being doubted by the Court insofar as fairness and integrity is concerned. It is possible and we are certain that the system ensures accurate electoral results.”

“It is, therefore, our considered view that having regard to the totality of the facts of the case and need to generate the greatest degree of satisfaction in all with regard to the full accuracy of the election results, the number of EVMs that would now be subjected to verification so far as VVPAT paper trail is concerned would be 5,” the apex court states in its order. As per the previous system, the EC would verify the 4,125 EVMs but now it will have to match 20,625 VVPATs, a process that is likely to delay the declaration of final results by at least 5-6 hours.

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