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The surveys may also have convinced Nenshi’s supporters he was in danger, causing them to show up at the polls in droves.

Like other observers, Henry said Mainstreet appears to have misread Nenshi’s support among younger voters, who were once again a major source of his electoral success.

Henry said his internal polling suggested that Nenshi had a 20-point lead among decided voters and saw that gap narrow as he lost ground during a nasty slugfest. But among voters aged 18 to 34, the mayor still had a 50-point lead Monday night, Henry said.

Nenshi’s base also includes many inner-city residents and northeast neighbourhoods, which are demographics that don’t traditionally vote as often as others, Henry said. But his team got supporters to the polls in large numbers.

“One of the flaws with (automated telephone) polling is they really don’t have a good measure of who the most likely voters are,” Henry said. “This was a peculiar election that this particular methodology was not well-suited in measuring.”

Mainstreet’s Maggi defended his firm’s methodology, arguing it used the same techniques to accurately predict the outcome of the Edmonton civic election, along with several other races conducted in Alberta in recent years.

Still, he acknowledged, “something was weird and wonky that got it wrong in Calgary.”

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Maggi said his team has three theories that could explain their inaccurate polling, including that it may have been able to get better results by offering surveys in other languages, as it has in places like Toronto.

The Calgary surveys may have also not taken enough samples from households that don’t have land lines and use only cells, which tend to be younger, more urban and “hip,” Maggi said.

A final theory, which the pollster believes could be the most significant, suggests voters may have been fatigued by negative robo calls from Smith’s camp, perhaps turning Nenshi supporters off from answering the phone.

Mainstreet expects to compile a report in the next month or so that will attempt to answer what went wrong with its Calgary predictions.

rsouthwick@postmedia.com