On the other hand, 1+1 might equal 3 - if a combined party looked more likely to achieve power. Like it or not, that's one of the biggest reasons people don't vote for third parties.

Anyway, I think my math is right. Let's test it.

From 1993 (the first election where Reform ran) to 2008, in every single election - except one, in 2004 - the PC vote plus the Reform (Canadian Alliance) vote was always around 37% - more or less the same as the merged CPC vote in 2006 and 2008

But under your logic, Stockholm, the merger should have scared off both hardened rightists and red Tories, creating a mass exodus. Never happened.