This graph tracks party proportionality in parliament.
The grey bar highlights periods of underrepresentation.
Parties with more seats than votes are above the grey bar.
Parties with fewer seats than votes are below it.
Points of interest
Note the significant dive of the PC party in 1993 corresponding with the appearance of the Reform party. This significant underrepresentation lasted 10 years until the 2003 merger. For historical context, see Stephen Harper's co-written 1997 article Our Benign Dictatorship.
Further, note the 2011 dive of the Liberal party and the sole instance of NDP over-proportionality. In this context, we see the 2015 Liberal platform explicitly calling to end first-past-the-post. The subsequent election won them a majority and the ability to follow through with this promise, though the promise was ultimately broken in 2017 with Trudeau's revised mandate for Gould.
Lastly, this data is only a summary. For a full picture, see the attached Jupyter workbook.