I wanted to determine how the swing in the by-election would play out on a national scale. To do so, I equally weighted 3 factors.
First, the most recent poll (picked over a poll average as it had a higher NDP number, and I wanted to compensate for the NDP's poor showing)
Second, the popular vote change from the last election in all 4 of the ridings.
Third, the popular vote change from the last election in the region each riding was in, the Pacific, the Prairies, Central Canada, and Atlantic Canada.
The final step was simply applying that ratio to all ridings in Canada, which produced this projection.
Note that I presumed that Singh would win his seat, as, his running, changes the math, and that previous by-election victories are applied to replace last-election results, which is how the Liberals retain Lac Saint Jean.
With this we get national totals of: