The EVM – VVPAT saga

by Abhay Bhatt and Rajeeva Karandikar.

There has been lot of grumbling in the Indian media about Electronic voting machines (EVM), esspecially over last 3 months, with opposition parties accusing the government of manipulating EVMs. This reached a crescendo recently when all the opposition parties joined hands and filed a petition in the Supreme Court seeking a directive to the Election Commission to cross verify the vote count reported by the EVM, with that of paper slips produced by the VVPAT (Voter verifiable paper audit trail), in 50% of the booths.

The Election Commission had consulted us about the sampling plan to be put in place to instill confidence about the sanctity of the election process. Here is our take on how to think about these questions.

The background

1. EVMs were first used in the Paravur Assembly constituency in Ernakulam district in the 1982 Assembly poll in about 50 booths. The CPI candidate, Mr. Pillai, defeated the Congress candidate, Mr. Jose, by a thin margin of 123 votes. Mr. Jose went to the High Court with the contention that the Representation of the People Act, 1951, and the Conduct of Elections Rules, 1961, did not empower the Election Commission to use EVMs. While the High Court dismissed the petition, subsequently the Supreme Court upheld the contention and ordered a repoll in these 50 booths. Mr. Jose won the election after this repoll.
2. Subsequently, the Representation of the People Act was amended, and S.61A was inserted, in December 1988, empowering the use of EVMs.
3. These EVMs were designed by public sector undertakings, BEL (a Defence Ministry PSU) and ECIL (an Atomic Energy Ministry PSU), who also manufacture the same. They are subjected to a thorough testing process.
4. The design and production are overseen by a technical expert committee consisting of senior professors in electronics and computer science from leading Indian Institutions.
5. The EVMs do not have any networking hardware. There is no ethernet port, no wifi or bluetooth capability, and thus it is not possible to alter or tamper the memory remotely.
6. The names of candidates on the EVM appear in an order that is determined by the same convention that had been followed since the sixties for the order on the ballot paper. First, the candidates of the national parties appear, in an alphabetical order of their names, then candidates of state parties (again in an alphabetical order of their names) and lastly the rest, again in an alphabetical order of their names. Thus, the order gets determined only after the last date of withdrawal of nomination.
7. The EVMs are distributed across the constituencies via randomisation. The EVMs used in India consist of two units: BU, the balloting unit and CU, the control unit. The BUs and CUs are distributed independently and on the day of polling, the two are connected. If one of them has been tampered or replaced, the handshake between the two units will fail and the pair will have to be replaced.
8. After the voting, the machine is locked by the presiding officer and then the EVM are physically sealed using the same techniques that were used to seal the ballot boxes of old.
9. In the parliamentary elections in 1999, EVMs were used in some constituencies and from 2004, all the elections to the parliament and to the state legislatures are conducted using the EVMs. It should be noted that in several instances, including in 2 out of three parliamentary elections – 2004, 2009 and 2014, the ruling party has lost the election.
10. The fact that there was no way to do a recount, even if a court ordered the same, was a reason for the Supreme Court to ask the EC to find a way of generating a paper trail. The Election Commission appointed a committee of experts, who came up with a design of the VVPAT machine and the Supreme Court ordered that the same be introduced as soon as possible for all elections.
11. The Supreme Court had not ordered the Election Commission to routinely carry out any cross verification of EVM and VVPAT count. The purpose of VVPAT was to have the possibility of a recount if a court so ordered, as a result of an election petition.
12. Since so many doubts had been raised about EVMs, the Election Commission decided that in every assembly constituency, one booth will be picked at random by a draw of lots and for the chosen booth, the VVPAT slips will be counted and cross checked with the count on the EVM. This done in order to increase public confidence in elections.

Our analysis of the recent debate

Over the last year, demands started coming up for verification of much larger number of EVMs. Various petitions were filed. The election commission engaged the two of us along with Mr. Onkar Prasad Ghosh to advise on an appropriate sample size, so if that many EVMs are randomly chosen and the machine count is verified with the VVPAT count and if no mismatches are found, then we can be confident that defective EVMs, if any, are in insignificant proportion.

We felt that given that the EVM's are assigned randomly to constituencies and that the order of names on the EVMs is determined at a late stage, only after the last date of withdrawal, it is not possible to manipulate or tamper the EVMs centrally.

Given that there is no networking component in EVM, tampering is possible only by getting physical access. If someone can get physical access to an EVM and tamper with the EVM, then the VVPAT slips can also be tampered and so validating EVM count by VVPAT count does not give any guarantee that EVM has not been tampered with. For this we must rely on the elaborate process that the Election Commission has about sealing the EVM in a bag, closing the same and storing in such a way that tampering can be detected. This was also the case with the paper ballot and ballot box method of earlier years. We are no worse with EVMs as compared with the old ways, in this regard.

Also, if some smart mind does figure out a way of changing the memory of EVMs remotely, he/she will not stop with doing so in one or two booths. Certainly, the effort will be to tamper with a larger number of constituencies so as to make an impact on the national level.

That is the reason that we took our objective to be to conclude with high degree of confidence that defective EVMs, if any, are less than a certain percentage of all EVMs in use nationwide. In our report we had taken this as 2%, but it can be 1% or 0.5%.

It is true that our suggested method does not give a guarantee at constituency level. But in our view, such a guarantee is not needed. Our sampling scheme can guarantee that the national picture has not been distorted by tampering or by a manufacturing defect. To those who have been insisting upon constituency level guarantees, we would ask: Why stop at the constituency? Should not every voter be assured that his or her vote has been counted correctly? The only way to do so without compromising privacy is to use cryptography. This is the subject of present research, with Prof. Bimal Roy, former director of ISI involved with one such initiative along with a team in UK. But when such a solution would become available, it can and will be attacked as opaque!

The Election Commission, in its affidavit to the Supreme Court, stated that in the last 2 years, over 1500 EVM counts have been matched with VVPAT counts and in all cases the matching has been perfect. Statistically, this alone is sufficient to conclude that EVM-VVAPT in use currently along with all the safeguards and practices in place are good.

We believe there is a lot of misinformation in the media. Various cases of EVM malfunction are being reported in the media and social media. These relate to local body elections or even college student union elections etc., which are outside the purview of the Election Commission. Other reports of EVM malfunction on the day of election are mostly about EVMs which fail the test before voting starts and are replaced.

While our recommendation was to draw a random sample from the population of all the EVMs in use, the EC decided to continue with their policy (for operational simplicity) to draw one booth per assembly segment, which translates to verifying 4125 EVMs by cross checking VVPAT counts. Based on the data about the number of booths across 4125 assembly segments, we were able to assert that if no defective is found in these 4125 chosen booths, we can say with 99.99999% confidence confidence that the proportion defective is less than 1%. This bound is true irrespective of the configuration of the defective EVMs. For example, a group of miscreants could have tried to tamper with EVMs selectively across a few constituencies. However, as long as the number of defective EVMs is 1% or more, the sampling procedure will catch this with a high probability.

The Supreme Court has ordered or suggested that instead of 1 per segment, 5 EVMs per assembly segment be drawn and VVPAT count and EVM count be cross verified. Based on our calculations, we conclude that if there are no defectives found in the 20625 randomly chosen booths (5 per assembly segment), then with 99.99999% confidence, the proportion of defectives, if any, are less than 0.25%, irrespective of the configuration of the defectives.


The authors are Professor, Indian Statistical Institute, Delhi and Director, Chennai Mathematical Institute, respectively.