WATERLOO REGION — Wondering why the leaders of Ontario's major political parties are stopping by Kitchener and Waterloo so often?

It's not just because they like early-morning runs in Victoria Park, sipping coffee at an independent cafe, or learning how to use a milling machine at Conestoga College.

The real reason NDP, Liberal and Progressive Conservative party campaign buses have circled both cities is polling data that suggests the riding of Kitchener-Waterloo houses the most competitive race in the entire provincial election.

Poll aggregator and critic Eric Grenier, operator of ThreeHundredEight.com, has combined results from all seven major polls that have been conducted in the province since May 2.

Between May 2 and May 15, the poll aggregation suggests all three candidates — incumbent Catherine Fife of the NDP, Tracey Weiler of the PCs and Jamie Burton of the Liberals — has led in the polls for a period of time.

It's the only riding in the province where three candidates have held the lead, according to Grenier's projections.

Between May 7 and May 15, the split between the three candidates ranged from 0.4 to 0.8 per cent, an extremely narrow margin.

Two other ridings, Etobicoke Centre and London West, have tighter margins, but only two parties are within striking distance of victory in each riding.

Grenier's projection weights newer polls and ones with larger sample sizes stronger than older, smaller ones, and corrects for factors such as incumbency.

Wilfrid Laurier University's Institute for the Study of Public Opinion and Policy says both Kitchener-Waterloo and Kitchener Centre are "too close to call," meaning the frontrunner and closest challenger in each riding are within three percentage points of one another.

Its projection uses the first three polls of the campaign and finds 13 of Ontario's 107 ridings are too close to predict a winner.