The first leaders' debate in the federal election campaign happens Thursday evening from 9 p.m. to 11 p.m. Atlantic Time. It will be hosted by Paul Wells of Maclean's Magazine.

Not everyone thinks a leaders' debate is the best basis on which to decide which party to vote for.

CBC Radio's Mainstreet asked a pollster, a Parliament Hill reporter, and a professor of policy studies how much debates matter.

Duane Bratt

Duane Bratt is the chair of and a professor in the Department of Policy Studies at Mount Royal University in Calgary.

Bratt says a lot of what happens in election debates is show biz, but they still matter, and sometimes they have a huge impact on election day results.

He points to the recent provincial election campaign in Alberta as an example.

"I think it turned the election around ... In most cases debates are not decisive, but in the Alberta case I thought it would be because all the leaders were brand new. And what happened is Jim Prentice for the first time in Conservative history decided to target the NDP ... And Notley handled herself very well, not only fended off Jim Prentice but in fact won the debate. And I think that just kept snowballing in the aftermath."

Éric Grenier

Éric Grenier is the founder of ThreeHundredEight.com, a website dedicated to political polling and electoral forecasts in Canada. He's working with the CBC during this campaign and has a weekly podcast called Pollcast.

Grenier says when you compare polling numbers before a debate and afterward, there's no doubt debates influence the electorate. And there doesn't necessarily need to be a knock-out punch.

"For example, the French language debate in 2011, Jack Layton's numbers, he was gaining a little bit before that debate, but afterwards he was picking up one or two points a day straight through to the end of the campaign in Quebec," he said.

Debates even influence people who don't watch them.

"In the last provincial election in Quebec, the leaders' debate, afterward the Coalition Avenir Québec from François Legault, his party made gains .... There was a poll that was done shortly after the debate was over, asking people who had not seen the debate who they thought had won it. And overwhelmingly these people thought François Legault had won that debate because they had seen all the media reports."

Elizabeth Thompson

Elizabeth Thompson is a senior writer with iPolitics.ca.

Thompson says debates are a great opportunity to see the leaders out of their usual element.

"We've seen them in question period, you know, going toe to toe. But question period's a very different format than a leadership debate. And while Tom Mulcair has become a master of question period, he really is untested when it comes to an election debate format because he did some debates when he was competing for the NDP leadership, but debates within a party tend not to be, you know, the gloves are still on a little bit ... because whoever wins, you don't want them too battered because they're going to be the leader of your party."