Do Opinion Polls Create Momentum in Political Competition?

While an informed electorate is generally considered essential for a well-functioning democracy, one exception concerns information provided through polls of candidates' relative standing. Critics claim that polls undermine both the incentive to vote as well as the vote itself; thus distorting voting decisions.

This ban can range from one day before the election, as in France, to a whole month before the election, as in Luxembourg.[1]

Scholarship has suggested several channels through which opinion polls may operate to alter voting decisions. They range from the desire of voters to cast a vote for the eventual election winner, over social learning, uncertainty aversion, to strategic voting and abstention. All of these have in common that they highlight a direct effect of polls on voters. What has been neglected so far is that polls also inform candidates about their relative standing during the campaign. This in turn influences the candidates' incentives to invest in their campaigns. Finally, these investments influence the voters' ballot choice on Election Day and thus the final election outcome.

In which way do opinion polls affect political competition? For the purpose of illustration, consider two equally skilled and ex-ante equally popular candidates concerned with winning the election. They campaign over a certain period of time and during this time random (unobservable) shocks to their popularity occur. Without a poll, candidates never learn about their current standing with the voter and thus at any point in time incentives are completely symmetric. With polls on the other hand, candidates receive updates about their current relative standing. This alters their incentives in the following way. A candidate who receives the information that she is ahead, now has an additional incentive to invest. The reason is that any additional investment now will afford her an even greater lead in expectation in the next poll. This in turn decreases the expected intensity and thus expected costs of future competition. A trailing candidate on the other hand has a weaker incentive to invest. Any additional investment now brings her closer in expectation to her opponent in the next poll and thus makes future competition more fierce and costly in expectation. Consequently polls drive a wedge between the investment incentives of the trailing and leading candidate and thereby create momentum for the front-runner.

When campaign spending is relatively effective and the candidates are in a close race, this intuition is valid for the trailing candidate as well. A large investment helps her overtake her opponent and at the same time defuses expected future competition. In these situations both candidates have an incentive to preempt the other with the objective to save costs in the future. In such situations we may observe momentum, but we may also observe the trailing candidate outspending and outperforming the front-runner.

In countries such as the Netherlands, where candidates are sufficiently interested in their vote share (and not only whether they can reach vote majority), the distribution of voters’ preferences becomes important. In a sufficiently polarized electorate a trailing candidate has stronger incentive to invest. The reason is that, due to polarization, competition is fiercest towards the ends of the voter spectrum, thus, moving towards the middle of the spectrum defuses competition and lowers expected future costs.

What can we learn from this about the welfare effects of polls? First of all, polls not only affect voters’ decisions directly. Thus a pre-election ban on the publication of polls will not eliminate all effects of polls as candidates may commission their own. Polls may favor the frontrunner or the trailing candidate, depending on the specifics of the voting environment. If a government wants to limit this biasing effect of polls, it needs to complement a ban on polling with restrictions on campaign spending. On the other hand, we also identify a positive effect of polls.  Note that initial asymmetries in popularity tend to be amplified through a poll. This has a mitigating effect on competition and thus leads to lower investments into the campaigns. Thus, polls tend to make campaigning less wasteful.

Additional information:

This article is based on a research paper with Philipp Denter with the title “Do Polls Create Momentum in Political Competition?”

More information

[1] The Netherlands has no restrictions in place.

Short bio of Dana Sisak
Since September 2011 Dana Sisak is an assistant professor in the Department of Economics at Erasmus School of Economics. also she is a candidate fellow at the Tinbergen Institute. Main fields of interests are Organizational Economics (especially relative incentives & social preferences, leadership, (self-)selection of talent) and Political Economy (especially political competition and the role of information).

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