Why you should ignore opinion poll seat projections

It is a truth universally acknowledged that Indian public opinion polls are much better at predicting party vote shares than they are at extrapolating to seats won in parliament or state assemblies. That’s because vote shares translate into seats in an unpredictable way under India’s multiparty “first-past-the-post” electoral system.

For example, the Indian National Congress (INC) increased its national vote share only 2% between 2004 and 2009 but its seats tally increased by 60 to 206. Uttar Pradesh is even more stark: the Bahujan Samaj Party won 206 seats in the 2007 assembly elections with more than 30% of the vote, but the Samajwadi Party won 224 seats in 2012 with only 29%. As Sanjay Kumar of the Centre for the Study of Developing Societies told The Caravan: “Same state, same voters, same parties. Party gets 1% less votes and gets 20 extra seats.”

The following chart from Rukmini Shrinivasan’s June 2013 article captures this unpredictability:


This means that people should take vote share projections in opinion polls much more seriously than seat share projections. And yet our TV studios and newspapers spend hours and column inches on seat predictions with only a cursory mention, if that, of respective vote shares.

So let’s take a look at what the four national opinion polls published so far in 2014 are saying about vote shares:

Screen Shot 2014-02-19 at 10.49.20 pm

The average of these four polls projects that vote share of the INC-led alliance will drop by 7% to 24%, that of the Bharatiya Janata Party (BJP)-led alliance will rise 13% to 34% and of others will fall 6% to 42%.

This is a sweeping vote shift by historical standards:

  1. If it occurs this would be the third biggest negative swing that the INC has suffered, smaller than the -9% and -11% swings in 1977 (post-emergency) and 1989 (Bofors, 1984 wave reversal) respectively but comparable with what occurred in 1996 after the Narasimha Rao government. Perhaps not so surprising in the current political environment.
  2. The real news is the 13% increase in the vote share of the BJP and its close allies, which surpasses the +4% swing in 1989 and the +9% swing the party experienced in 1991 after the Ram Temple movement. This is particularly surprising given the absence of the BJP from large swathes of southern and eastern India.
  3. The fall in the vote share of others is also noteworthy given the rise of the Aam Aadmi Party and the resilience of regional parties in Andhra Pradesh, Bihar, Tamil Nadu, West Bengal and elsewhere.

I will look into these numbers in greater detail in the near future, but here are two caveats:

  • With the exception of the BJP, party campaigns only picked up recently. Not all voters may be paying attention at this point and late vote swings have been known to occur.
  • Candidate selection and quality are important, which is why early polls can be misleading.

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