If you want to know why Forum Research’s poll is out of line with the other polls done on the provincial election, you need look no further than the data tables for the questions.
This is why pollsters should give out this information. Lots don’t.
Polling firms adjust their sample so that the sample matches the population as a who for sex, age, geography, and so on. It’s called weighting.
Forum notes that where “appropriate, the data has been statistically weighted by age, region, and other variables to ensure that the sample reflects the actual population according to the latest Census data.”
That’s where you get the problem.