VVPAT-based audit of EVMs
It is a typical case of “lot acceptance sampling”, a statistical quality control technique widely used in industry and trade.
If the number of defectives found in a randomly drawn, statistical sample is less than or equal to a specified ‘acceptance number’, the entire lot (or ‘population’) is accepted; otherwise, the entire lot is rejected.
We define a ‘defective EVM’ as one which has a mismatch between the EVM count and the VVPAT count due to EVM malfunction or manipulation.
We specify the acceptance number as ‘zero defective EVM’.
A solution
The Supreme Court did not specify the ‘population’ of EVMs to which its sample size relates and the ‘next steps’ in the event of a ‘defective EVM’ turning up in a sample.
The Election Commission of India (ECI) has also chosen to leave them vague.
Both these are important because in the event of one or more ‘defective EVMs’ turning up in a sample, the entire ‘population’ from which that sample was drawn should be ‘rejected’.
In other words, manual counting of VVPAT slips should be done for all the remaining EVMs of that particular ‘population’ and its results declared based on VVPAT count only.
Statistical sampling theory tells us that the probability that the Court-mandated sample size will fail to detect a ‘defective EVM’ is 95% if ‘EVMs deployed in an Assembly Constituency’ are defined as the ‘population’, and 70% if ‘EVMs deployed in a Parliamentary Constituency’ are defined as the ‘population’.
This defeats the very purpose of introducing VVPAT
What we need to do is implement a statistically sound VVPAT-based system of EVM audit which can detect instances of mismatch with 99% or 99.9% accuracy.
The matching exercise should be done at the beginning of the counting day. Not at the fag end.
Where there is a perfect match, the results should be declared based on the EVM count.
Only where there is a mismatch, should manual counting of VVPAT slips for all the remaining EVMs of the particular ‘population’ be done and its results declared based on the VVPAT count.
This statistical sampling-based, ‘management by exception’ approach represents the golden mean.
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