DW: Opinion polls were wrong about the Brexit referendum, the US presidential election and the Dutch parliamentary elections. What does this mean for the presidential vote in France?

Stephane Wahnich: As pollsters, we currently do not know what we are calculating. Unlike in Great Britain or the US, opinion polls in France are calculated on the basis of the last elections, meaning in 2012. Five years ago, roughly 50 percent of the electorate voted for the right and 50 percent for the left. Today, it's different. That is why we run the risk of a surprise in France.

The latest polls show that Marine Le Pen has no chance of winning the runoff ballot. Right-wing candidates are often underestimated in surveys. Is this also possible in France?

Yes, it is even highly probable. Polls currently have Marine Le Pen from the National Front at 24 percent. I'm assuming that it will more likely be around 30 percent in the first ballot. This is also due to the fact that right-wing voters do not tell pollsters whom they will vote for. Le Pen and Macron both are not part of France's traditional political system. That is why it is possible that many voters may say that they will vote for the moderate one of the two, meaning centrist [Emmanuel] Macron, but then actually vote for Le Pen on the day of the election.

The polls say that Macron is the sure winner against Le Pen in the runoff. How likely is that to happen?

We certainly can expect a surprise. That does not mean that Marine Le Pen will win. A survey on the possibility of a second ballot between the liberal Macron and the right-wing populist Le Pen has Macron at around 60 percent and Le Pen at 40 percent. The final outcome will probably be closer.

Can we still assume that Le Pen will not be France's next president?

No, this cannot be ruled out with certainty. If polls continue to tout Macron as the clear winner in a second ballot against Marine Le Pen and if the press also convey this as well, then things could turn out differently. I am very cautious about that. The predictions that say Macron will be the clear winner could cause many potential Macron voters to not go to the polls for the second ballot. As a newcomer to politics, Macron has no voter base he can depend on. Marine Le Pen and the National Front, on the other hand, have loyal supporters. This could even lead to a big surprise and Le Pen may be elected president.

The current frontrunner Macron was practically unknown in 2012 and his "En Marche" ("Forward!") movement was just founded last year. What problem does being a newcomer pose?

We lack the information basis from 2012 for Macron. Current figures show that a trend for him and his "En Marche!" movement is emerging. However, we do not know exactly what we are calculating. I personally fear that Emmanuel Macron is overrated in the polls. He is at 24 percent at the moment. This actually would mean that voters who voted for the conservative party in 2012 are now voting for Macron. I have a hard time believing that. If the polls are actually wrong, Macron could end up getting 8 to 10 percentage points less than predicted.

So far, the election campaign has been influenced by scandals involving candidates and the rifts in the left. What role will undecided voters or non-voters play in this election?

We have more undecided voters in France. About a quarter of French voters decide on the day of the elections. That means when we ask people who they will vote for, they have still not decided for whom they will cast their ballots. This is problematic for opinion researchers. The French electorate is no longer unwavering. Our society is changing. It makes it hard to make reliable forecasts. When you consider this, then surveys are completely overrated in this election campaign.

The numerous scandals involving some candidates have led to the fact there has been no deep-reaching debate on the election platforms. Only now are voters beginning to think about policies. This is obvious in the fact that the distribution of votes between the candidates has slightly shifted. Macron and Le Pen, the two "anti-establishment" candidates, are seeing slight losses, while other candidates are gaining single percentage points. We cannot predict which way this trend will develop. It will probably take shape in the week before the election.

How accurate were polls in the last French elections?

In the last elections in 2012, the polls were well off the mark. The forecasts for the moderate left and the moderate right were correct, while the forecasts for the extreme left and the extreme right were wrong. On the left, Jean-Luc Melenchon had been expected to win more votes than he actually received. Marine Le Pen benefited from those votes. Because of that, Marine Le Pen achieved a historic result five years ago; even if it did not seem so in the polls. I fear that in 2017 we will see a similar pattern.

Stephane Wahnich is the general director of the "SCP Communication" research institute in Paris and an associate professor for political communications at the University of Paris Est-Creteil (UPEC).

The interview was conducted by DW's Doris Pundy.