Although the existence of strategic voting in the United Kingdom and Canada has been well documented, quantifying when a voter will cast a strategic ballot has yet to be done. This article draws on electoral data from five UK and Canadian elections in order to address this gap by identifying a precise “tipping point” for when a non-viable party supporter's probability of voting strategically crosses a 50 per cent threshold. I find the best tipping point measure occurs when a voter rates their favourite viable party greater than 59 out of 100 in the UK and greater than 73 out of 100 in Canada. Both countries also have clear tipping points for the likeability of an individual's highest preferred party and perceptions of that party's distance from contention. Overall, by calculating these tipping points, researchers can better gauge voter behaviour and how, or when, certain factors contribute to strategic voting.

In this article, we study how polarization affects the propensity of supporters of non-viable parties to cast a strategic vote. To do so, we rely on Canadian election panel surveys from the Making Electoral Democracy Work project that were specifically designed to identify strategic voting. We find that the polarization between viable parties increases the probability of a supporter of a non-viable party casting a strategic vote, because it increases how much she likes her favourite viable party, and decreases how much she dislikes her least favourite viable party. Polarization thus increases strategic voting because it alters partisan preferences.