A week from election day, Conservatives still had a shot. What happened?

The Conservatives entered election day trailing the Liberals by only 16 seats and ahead by more than three percentage points on the votes that had been cast already in the advance polls — but then lost their lead in a dozen seats on election day as the Liberals strengthened their minority and the New Democrats avoided disaster.

According to a CBC News analysis of the detailed validated results provided by Elections Canada, the Conservatives put up strong numbers in the advance polls but failed to get their vote out in similarly large numbers on election day in almost every region of the country.

That resulted in seat losses that benefited the Liberals. It also helped out the New Democrats, who experienced a big boost in support on election day compared to their anemic advance poll results.

Advance voting was held between Oct. 11 and 14, giving voters a chance to cast their ballots ahead of election day on Oct. 21. Some 4.8 million Canadians exercised this option, representing roughly 27 per cent of all ballots cast.

Compiling the individual results of each advance poll for all 338 ridings reveals that Justin Trudeau's Liberals were leading in 149 seats once the advance polls were over, while the Conservatives were ahead in 133 seats. That 16-seat gap between the two parties was less than half of the 36-seat margin that separated the two parties when all the votes were finally counted.

The Bloc Québécois was leading in 33 seats in the advance polls, followed by the New Democrats with just 19 and the Greens with three. Independent candidate (now MP) Jody Wilson-Raybould was also leading in the advance poll in her Vancouver Granville riding.

The Conservatives took the largest share of votes overall in the advance polls: 36.3 per cent of ballots cast over the Thanksgiving weekend, outpacing the Liberals' 33 per cent. The NDP was well behind with just 13.3 per cent of the advance poll, followed by the Bloc at 8.6 per cent (34.4 per cent in Quebec, putting them first in the province), the Greens at 6.6 per cent and the People's Party with 1.5 per cent.

So a week out, the prize was within reach for Andrew Scheer's Conservatives; the party was trailing the Liberals in the advance polls by just four points or less in enough ridings to put them ahead in the seat count if they could win those on election day and hold their lead in the other 133 seats. Instead, they came up short.

Conservatives faltered on election day

Counting only the ballots cast on Oct. 21 — excluding both the advance poll results and special ballots — the Liberals had the most votes in 155 seats, the Conservatives in just 118.

The Bloc was on top in 34 seats on election day, with the NDP taking the most votes in 27 and the Greens in three. Wilson-Raybould also won Vancouver Granville on election day.

The Conservatives only narrowly edged out the Liberals in votes cast on Oct. 21, taking 33.6 per cent compared to the Liberals' 33.2 per cent. The NDP took 17 per cent of ballots cast on election day, followed by the Bloc at 7.4 per cent (31.9 per cent in Quebec, putting them behind the Liberals), the Greens at 6.4 per cent and the People's Party at 1.6 per cent.

This suggests that while the Liberals took roughly the same amount of the vote in both the advance polls and on election day (there's a difference of only 0.2 percentage points), the Conservative vote dropped by 2.7 points. Jagmeet Singh's NDP saw the biggest jump, taking 3.7 points more on election day than they did in the advance polls.

Where election day made the difference

There were a dozen ridings where the Conservatives' performance on election day cost them the seat — ridings where their lead in the advance poll was not wide enough to compensate for poorer results on Oct. 21.

This boosted both the Liberals and the New Democrats. Largely due to the Conservatives falling back on election day, the Liberals picked up King–Vaughan, Kitchener–Conestoga and Richmond Hill in Ontario, Winnipeg South in Manitoba, Coquitlam–Port Coquitlam in British Columbia and Yukon in the North.

The NDP's election day boost pushed them ahead of the Conservatives in Elmwood–Transcona in Manitoba and Skeena–Bulkley Valley, South Okanagan–West Kootenay and North Island–Powell River in British Columbia. The NDP also was able to beat the Liberals in Windsor West in Ontario and the Greens in Victoria, B.C. on election day.

While the Greens lost Victoria, they made up for it with a gain in Fredericton, where the Conservatives had been leading after the advance polls. The Bloc also took Beauport–Limoilou away from the Conservatives on election day.

But the Liberals bolstered their own minority with wins in Quebec on Oct. 21. The party had been trailing the Bloc in Hochelaga, Longueuil–Charles-LeMoyne and Québec after the advance poll. They pulled out a win in these three ridings on election day (though the opposite happened in Shefford, where the Bloc stole a riding where the Liberals led in the advance poll). They also came from behind in the Ontario riding of Davenport, where the NDP had been ahead after Thanksgiving's voting.

Where the advance poll mattered

In a few ridings, meanwhile, the advance poll made the difference. In the Quebec riding of Chicoutimi–Le Fjord, the Ontario riding of Kenora and the B.C. riding of Port Moody–Coquitlam, the Conservatives built up enough of a lead in the advance poll to stay ahead despite finishing second on election day itself.

In 29 ridings, the Conservatives even managed to win enough of the advance polls to leave them in a position where they didn't need more votes on election day itself. All of those ridings were in Western Canada — 22 in Alberta, six in Saskatchewan and one in B.C.

The Liberals enjoyed the same level of advance poll success in just four ridings, all in Quebec. Meanwhile, their advance poll results allowed them to prevail in Gaspésie–Îles-de-la-Madeleine in Quebec — despite losing election day itself to the Bloc — and Windsor–Tecumseh in Ontario, where the NDP took more of the vote on election day.

Ground game or a change of heart?

The differences between the advance poll and election day results could be explained in part by the parties' ground games; parties with better voter outreach operations tend to be more successful at getting their supporters to cast ballots early.

Those differences also offer a glimpse of how undecided voters might have moved in the final week of the campaign.

Hamish Marshall, the Conservatives' campaign manager, told CBC News in an interview last week that he had been confident after the advance poll, but that there was a noticeable drop in "voter enthusiasm" for his party in the last week of the campaign. These numbers tend to support his version of events.

The Conservatives took less of the vote on election day than they did in the advance polls in every region of the country except Atlantic Canada. The drop was steepest in the Prairies — which might suggest that anti-Liberal voters in the region had their minds made up early. That drop didn't do them any damage in the region, but it did hurt them in British Columbia and Ontario.

The New Democrats, who were riding a wave of optimism in the final stages of the campaign, did get a boost on election day compared to the advance polls, winning a number of seats in the process. Had they failed to pick up these extra seats on election day, the NDP might have fallen just short of holding the balance of power in the House of Commons.

But the Liberals were the biggest beneficiaries. Their vote held up. The Bloc and Conservative vote did not, and it helped deliver enough seats to the Liberals to give them a firm grip on a minority legislature.

One week out, the Conservatives were still in the running to win. It was the day that mattered most that cost them their chance.