In CBC's poll tracker, why do the probabilities of winning not add up to 100%?

1

In CBC's poll tracker at: https://newsinteractives.cbc.ca/elections/poll-tracker/canada/, probabilities of winning the 2019 Canadian federal election are provided.

Currently, these are 11% Liberal majority, 39% Liberal minority, 42% Conservative minority, and 6% Conservative majority. By my count, these probabilities add up to 98%. Shouldn't this be 100%?

Answers

5

I don't see any explanation on their Full Methodology Info page, but when percentages don't add up to 100%, the usual answer is that it's due to rounding, so 11% might actually be 11.4%, which was rounded down to 11. Among 4 options, rounding could explain almost all of the missing 2%.

Another possibility, is that these 4 options don't represent all possibilities. For example, it's possible that the Liberals and Conservatives get equal numbers of seats, but neither has a majority (due to seats gained by other parties)

Indeed, I can see the extra 1-2% being a tie. – Joe C – 2019-10-15T18:10:10.197

I thought of a third party (such as the NDP) winning as a possibility for making up the 1-2%, but that seems to be ruled out by the fact that their maximum projected seats is only 60. The possibility of a rounding down or a tie makes sense though. Thanks. – Jimmy Vailer – 2019-10-15T19:09:07.330