Arthabaska:
There only the PQ basically held its level of support from 2014. 16,77 % on Monday compared to 17,07 % in 2014. The PQ did BETTER than all the other major parties in Arthabaska.
The CAQ may have won but went from 45,49 % to 43,96 %,
The Liberals who dreamed of taking the riding from CAQ went from 30,21 % in 2014 to 27,56 % Dec. 5 and 
QS fell from 5,21 % to 3,61 %
Why ?
There was a spoiler, a Conservative candidate who took 4,7 % of the votes on Monday compared to 1,11 % for their candidate in 2014. In 2015 the MNA for Arthabaska, Sylvie Roy quit the CAQ and became an independent. Her death prompted the by election. Did some of her loyalists refuse to go back to CAQ ?
December 5 was not a happy day for François Legault. 
The CAQ lost support in three of the four bye-elections and failed to take back St-Jérôme, a seat they had won in 2012. 
Despite the upticks for QS in Verdun and Marie-Victorin, QS declined outside of Montreal & suburbs, falling to 5th place in Arthabaska.