Princeton Election Consortium

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Can voter ID laws affect the Presidential election?

July 14th, 2012, 7:13am by Sam Wang


In a very close race, voter ID measures could affect the outcome. In the extreme scenario, it could flip the Presidential election. How?

About 10% of Americans currently lack government-issued ID. This is a Democratic-leaning population. The percentage is higher among African-Americans. States that have new voter requirements include Pennsylvania, Florida, Iowa, Virginia and Ohio. This is disconcerting considering the fact that there is basically no evidence for voter fraud being a significant factor in US elections.

About 9% of Pennsylvania’s ~9 million registered voters lack a government ID. Pennsylvania’s in-person requirements for voter ID and provisional voting are here. If all of those votes are lost and they break 2-1 Democratic, that would be a net gain of up to ~3% for Romney. The current margins for Pennsylvania are Obama +7%. My guess is that if this margin drops to +3% or below, then Republicans have some chance to flip the outcome there.

Can this be accounted for in the Meta-Analysis? In a limited manner, yes. One way to give you a sense of the maximum possible impact of voter-ID laws is the “+2% for Romney” tool in the right sidebar. Another view comes from using the Meta-Margin, whose accuracy is a few tenths of a percentage point. It’s at Obama +3.0%, right on the edge for a Republican win if they get voter-ID laws in all swing states and if they extract the maximum possible advantage (and if pollsters somehow failed to assess this).

Pollsters will eventually take the new requirements into account in their likely-voter screen. They can ask questions such as “Do you have a government-issued picture ID?” At some level, it feels best to leave that to them.

Thanks to Rachel Findley for suggesting this question.

Tags: 2012 Election · Politics · President

6 Comments so far ↓

  • Bill N

    I have a quick question. What degree of confidence, if any, should be given to the apparent trend in the EV graphic? It appears to be trending downward, in the direction of Romney gaining EVs. Should any significance at all be attributed to this apparent trend?

  • Sam Wang

    Bill N, state polls are so sparse right now. The current estimate is still within the range for the last 30 days. If the estimator dips to 295 EV or below, or if the Meta-Margin gets below 2.0%, then the trend is probably real. Give it a week.

    It will be interesting to see if there is an effect of all the press regarding Mitt Romney’s statements about Bain and his tax returns.

    In 2008 I thought that Obama’s foreign policy trip would have an effect, but it did nothing, nor did the converse “Celebrity” ad. (The 2008 EV graph will be clickable in a few days and you can see for yourself.)

  • Bill N

    Thanks for your response. The very wide confidence intervals make it challenging to try and interpret any apparent trends. There is the long term trend from the beginning of the graph, and then there is the very short trend at the far right end.

    It will be interesting to see if there are any effects of the Bain stories and the tax return controversy. I have thought for a while that this is Romney’s election to lose given the poor economy, and the huge amounts of super pac money that will be fueling negative ads against Obama. Give your past work in this area, what kind of lag would you expect to see between the Bain and tax controversies and a change in the EV patterns?

    • Sam Wang

      That’s not true. I’m going to be de-emphasizing those. The true CI is a fraction of the displayed, nominal error. It has to do with the fact that systematic pollster-to-pollster variability is included, yet these variabilities cancel one another. Think of the true error as being about 1/4 what is shown.

  • William Lonie

    What percentage of the registered voters without id are non-citizens?

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