From November to February, more than nine million names were deleted from the Bengal electoral rolls in the space as part of what the Election Commission of India calls a Special Intensive Revision.
This was followed by a shock landslide win by the Bharatiya Janata Party on May 4, where the Hindutva party won 70% of the seats in the Assembly.
In this piece, we use statistical methods to examine whether SIR deletions were associated with electoral outcomes. We also build a simple model to try and quantify the extent of the impact.
Our analysis shows a strong relationship between SIR deletions and electoral performance in Bengal: constituencies where the electoral roll shrank more also saw the BJP do better relative to its main challenger, the Trinamool Congress. Notably, a comparable exercise in Bihar, which also underwent an SIR, shows no equivalent pro-ruling alliance pattern linked to roll shrinkage.
Our method
We seek to find the relationship between voters deleted during the SIR and the relative performance of the BJP and Trinamool: the two main players in this election.
This approach differs from much of the existing discussion, which compares the number of deleted voters with the final winning margin. In our view, that arithmetic misses how rolls actually shape elections. Roll deletion does not merely subtract names from a list. It can change the composition of the electorate that remains, the balance of local coalitions and the signals voters and parties read about who is strong.
The better test, then, is whether roll shrinkage was systematically associated with changes in party margins.
To do this, we must understand the relationship between roll shrinkage and the relative electoral performance of the BJP vis a vis the Trinamool, using Assembly constituency level data.
In West Bengal, “all-cause” roll shrinkage is measured as the percentage fall in total electors from the 2024 Lok Sabha divided by assembly segments to the final post-SIR roll before the 2026 Assembly election. For example, in Kolkata’s Bhabanipur assembly constituency, the number of electors shrank from 2,05,553 in the 2024 general election to 1,60,313 in the final post-SIR roll before the 2026 election – a roll shrinkage of 22%.
“All-cause” means the total fall in registered electors, whatever reason was recorded for deletion. It includes valid removals like deaths, migration, duplicates but can also include erroneous removals of eligible citizens. It is, therefore, simply a measure of how much the formal electorate contracted over the administrative exercise.
What we are tracking is the relative change in the electoral performance of the BJP vis-a-vis the Trinamool from 2021 to 2026. We measure this as the change in the BJP minus Trinamool vote share from 2021 to 2026. If it becomes less negative or more positive, the constituency has shifted toward the BJP relative to the TMC.
For example, in Bhabanipur, the BJP received 35.2% of the vote in 2021 and the Trinamool received 57.7%, giving the BJP a margin of −22.5 percentage points. In 2026, the BJP received 53.0% and the Trinamool received 42.2%, a margin of +10.8 points. The constituency thus moved 33.3 percentage points toward the BJP relative to the Trinamool.
We replicate the same logic for Bihar, another state where parties raised concerns about the SIR process. There, all-cause roll shrinkage compares the 2024 Lok Sabha elector count divided by assembly segments with the 2025 Assembly elector count. The electoral outcome is the change in the BJP-led National Democratic Alliance minus the opposition Mahagathbandhan margin between the 2020 and 2025 Assembly elections.
Because Bihar’s alliances changed over this period, we rebuilt National Democratic Alliance and Mahagathbandhan vote shares from party-level results separately for each year, using year-specific alliance membership.
The data cannot establish intent behind deletions, nor show how deleted voters would have voted, but they can tell us whether the geography of roll shrinkage lined up with the geography of electoral change.
What the data shows
The first difference between Bengal and Bihar is the scale of deletions (see Figure 1).
In West Bengal, the median constituency saw roll shrinkage of 9.6% – which means half the constituencies had lower shrinkage and half had higher shrinkage.
Bihar’s median, on the other hand, was only 3.0%. Positive values mean the electoral roll got smaller. This does not prove that any particular deletion was improper. It just shows that Bengal’s contraction was much larger – all the more stark given that the West Bengal election was a year later, and the rolls should have gained an extra year of newly registered voters.
Figure 1: Distribution of roll shrinkage in West Bengal and Bihar. The figure shows a histogram where the x-axis shows the percentage fall in registered electors from the 2024 Lok Sabha assembly-segment roll to the later Assembly roll; positive values mean the roll got smalle…
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