Let's start with the most important point.
Predicting a by-election result is sometimes more difficult than forecasting who will win a seat in a general election.
That's because the importance of certain variables—like the possibility low voter turnout and the lack of risk in citizens casting protest votes against the government—elevate the uncertainty.
Add to that the popularity of the Greens on Vancouver Island and the creation of the far-right People's Party of Canada under Maxime Bernier, and predicting the outcome tomorrow's Nanaimo-Ladysmith by-election becomes even murkier.
With all of this in mind, here are three things to think about as you watch the results coming in on Monday (May 6) night:
1. Northern part of the riding is conservative
Nanaimo-Ladysmith was created in 2015 by combining 44 percent of the former riding of Nanaimo-Alberni with 55 percent of Nanaimo-Cowichan to the south. Nanaimo-Alberni was a safe Conservative, Canadian Alliance, and Reform seat dating back to 1997.
Voters in the northern part of the riding tend to be older; many have worked in the resource sector; and they can be more attitudinally conservative than those living on Gabriola Island, downtown Nanaimo, and Cowichan.
If Conservative candidate John Hirst is able to perform exceptionally well in the northern part of the riding even as he's being challenged by People's Party of Canada candidate Jennifer Clark, he could emerge victorious.
The outcome could be determined by how votes split between Green candidate Paul Manly and NDP candidate Bob Chamberlin in the southern section, which has gone strongly NDP in the past.
2. NDP machine often triumphs
In the last Nanaimo provincial by-election, a Mainstreet Research poll showed B.C. Liberal Tony Harris with a substantial lead over New Democrat Sheila Malcolmson. Yet she won by nearly 2,000 votes as the Green candidate only attracted 7.4 percent support.
Chalk it up to the powerful NDP machine in Nanaimo. It was able to identify potential supporters and get them out to the ballot box in ways that the Greens could only dream of.
The growth of Vancouver Island University has also helped give Nanaimo a more urban vibe—and urban areas, with a few exceptions, tend not to support the Conservatives.
NDP candidate Bob Chamberlin is a credible and articulate flag bearer for his party. So even though a Green party poll claims that Manly is in the lead, that could turn out to be as meaningless as the Mainstreet Research poll last January.
3. Turnout matters
Nanaimo-Ladysmith had a sky-high turnout in 2015 at 75 percent. While nobody is expecting that to be replicated in a by-election, higher-than expected turnout could help the Greens, People's Party of Canada, or the Liberals, which don't have as well-developed political machines as the Conservatives and NDP.
About 9,000 voters showed up for the advance vote, which was held over four days in late April. While that sounds like a high number, it's lower than the number who voted early in 2015.
Green candidate Manly's father Jim was a popular NDP MP on Vancouver Island in the 1980s. And the Greens did exceptionally well in the last Prince Edward Island provincial election, becoming the Official Opposition.
One area to keep an eye on will be Gabriola Island, which has slightly more than 4,000 voters. It could be a bellwether of the level of support for the Greens.
If residents there abandon the NDP because they're dissatisfied with the provincial government's record on climate change, it could spell trouble for Chamberlin on election night.
Another area to watch will be the Cowichan Valley. Previously an NDP stronghold, voters there elected a Green candidate, Sonia Furstenau, to the B.C. legislature in 2017.
The Liberals have never fared well in recent years on the mid-Island, so it will take a stunning turnaround for the party's candidate, Michelle Cornfield to buck that tide.
It's hard to imagine this riding going the way of the South Surrey–White Rock by-election in 2017, where Liberal Gordie Hogg captured the seat. That's because South Surrey and White Rock are two communities where NDP support has traditionally been weak—enabling the Liberals to vacuum up the progressive vote to thwart the Conservatives. That's certainly not the case in Nanaimo.