Tuesday was the last day for people who want to vote in the Conservative leadership race to buy a federal party membership.

By the end of the week, some campaigns were disclosing how many new supporters they'd signed up, perhaps seizing an opportunity to try to keep supporters donating and motivated ahead of the May 27 vote.

Their boasts can't be officially verified. The party will only be revealing the total number of members eligible to vote, and that number isn't ready yet.

Here are a few more reasons you may want to keep a salt shaker handy so you can take these claims with a few grains.

Memberships aren't votes

Signing up someone, or persuading an existing member to support a candidate, is only the first step. Campaigns have to close the deal and get these Conservatives to vote.

Turnouts from recent leadership elections illustrate the challenge.

Both the 2004 Conservative race that picked Stephen Harper and the 2013 Liberal race that picked Justin Trudeau saw roughly a third of eligible members vote. The NDP fared a bit better when Thomas Mulcair was chosen in 2012, when just over half turned out.

It may be a few weeks before party officials verify new memberships and confirm how many are eligible to vote. Each candidate will then be given the membership list.

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Several camps submitted memberships at the last minute to keep the names of new supporters secret for as long as possible, giving rivals the shortest possible window to try to steal the support of their new recruits.

Estimates percolating among people watching the race now have total memberships at about 150,000 at the low end, and beyond 180,000 on the more optimistic side.

That compares to the 100,000 members the party confirmed two months ago.

Some polling has tried to measure support among existing members. Pollsters haven't had access to lists of new members from rival camps, but it's important to know where candidates stand with the loyal base because party faithful are likely to turn out.

When someone like Kevin O'Leary says he's signed up more than 33,000 new members, it's hard to know how significant that is.

Other camps, like that of Erin O'Toole, say they won't release their numbers.

Voting disincentives

After controversies two weeks ago over improper membership sales, it's worth talking about how the party will ensure each vote cast represents a genuine supporter.

There are two ways to vote, and both may be inconvenient or unappealing for some members.

Any riding association that wanted to could have organized a polling station. Only a few did.

Only three are west of Ontario: two in Winnipeg and one in Edmonton. Only one is in Quebec (in Montreal). The only place you can vote in person in Atlantic Canada is in Moncton.

There will be eight polling locations in Ontario:

Ajax (candidate Chris Alexander's former riding, but also a short drive from Erin O'Toole's).

Carleton/Kanata–Carleton (two Ottawa-area ridings sharing a poll).

Milton (Lisa Raitt's riding).

Niagara Falls.

Simcoe–Grey (Kellie Leitch's riding).

Three ridings close to Michael Chong's base: Cambridge, Kitchener–Conestoga and his riding of Wellington–Halton Hills (Milton isn't far either).

Members attending the leadership event at the Toronto Congress Centre can also vote in person on May 27.

Maxime Bernier is thought to be one of the front-runners in the race. He usually wins his rural Quebec riding by a large margin, but his hometown supporters will have to drive to Montreal or mail in their ballots. (Codie McLachlan/Canadian Press)

For everyone else everywhere else, getting out this vote means mailing in ballots.

Voting packages go out later this month. But some organizers have expressed concerns that mail-in votes might also be difficult to turn out.

Members have to mail a photocopy of valid identification along with their ballot.

Is it convenient for everyone to photocopy their driver's licence or health card? Will voters be comfortable, for privacy reasons, sharing a passport scan with a political party?

Ridings are equal

On Thursday, Chong's campaign said it had sold 17,000 new memberships: "That puts us on the path to victory," supporters were told.

In an interview with Rosemary Barton on CBC's Power & Politics, Chong laid out how his campaign settled on that figure.

Only 5,000 of those memberships were actually purchased directly through his campaign website, he said. The rest is essentially a guesstimate. "People tweeted us, Facebooked us and messaged us to say they signed up."

He said, all told, they "expect" about 5,000 people who purchased their memberships through Conservative.ca will back his leadership bid.

Another 7,000 memberships were sold on "organic websites that sprung up during the campaign," he said. Indeed, some progressive voters have joined the party to vote for Chong to stop the likes of Kellie Leitch from winning the nomination.

Earlier in the week, Raitt claimed to have sold more than 10,000 memberships and Leitch more than 30,000.

But were those concentrated in a few ridings, or spread evenly across Canada?

This matters because the 338 ridings are weighted equally in this race.

While it might seem impressive to turn out several thousand votes in a few ridings, that may be no more significant than a dozen votes in other ridings with short membership lists.

Ranked ballot strategy

This isn't a first-past-the-post election. Instead, voters can rank up to ten candidates on their ballot.

With 14 running and no obvious front-runner, a candidate is unlikely to win with only first-choice votes.

Candidates Michael Chong and Lisa Raitt come from neighbouring ridings and have been competing for many of the same potential supporters in the Greater Toronto Area. Voters' second or third choices will matter in this race. (Paul Chiasson/Canadian Press)

Being someone's second choice will be valuable because the ballot process drops candidates with little support and reallocates their backers' second (or third, or even fourth) choices until someone has at least 50 per cent support.

Sign-up stats don't tell us anything about second- or third-choice appeal.

Since it's not against the rules to support several candidates (and rank them 1,2,3) there's a chance some campaigns may be counting the same people as they track supporters.

There's also been some "anyone but" campaigning, where organizers ask people who don't normally vote Conservative to join and stop a candidate they dislike.

Is any of this numerically significant? Hard to say. But with so many contenders, this race may come down to small margins.

Feelings change

A few parliamentarians have changed their endorsements of candidates, either because they haven't liked what they've seen from a candidate, or, in at least one case, pledged support too early before someone else they liked better entered the race.

Happy to welcome Conservative Senate Caucus Chair <a href="https://twitter.com/wellsdavid">@wellsdavid</a> to the growing <a href="https://twitter.com/hashtag/TeamOleary?src=hash">#TeamOleary</a>. The momentum isn't slowing down! <a href="https://twitter.com/hashtag/cdnpoli?src=hash">#cdnpoli</a> <a href="https://twitter.com/hashtag/cpcldr?src=hash">#cpcldr</a> <a href="https://t.co/jCXarL8G8U">pic.twitter.com/jCXarL8G8U</a> —@kevinolearytv

Voters, too, can change their minds. Just because a campaign signed them up, doesn't mean that vote's locked in.

Campaigns faced a small fee for memberships they signed up in the final month: an incentive to avoid swamping the party at deadline.

CBC News has heard anecdotes about people signing up on websites of candidates they don't support to save money for the candidate(s) they do like.