Pedant, Milnews, but also incorrect (which makes it worse ;D).
The +/- error is not something you can apply as you wish to increase someone's number or decrease someone else (i.e. you can't say that the poll shows the NDP just as likely at 33% [36-3] than the Libs at 35% (32+3).
The plus minus error figures are non-distributive mathematical model errors: this means that (if you pair it with the 19 times out of 20 factor, known in maths as the 95 percentile confidence factor) if you polled the same number of Canadians, at random, 20 different times, on that same day, you could find different results for each party that would fall within the figure released + or - 3%, and the last survey would bear no such resemblance with such distribution at all. However, the further you are in the outliers (i.e closer to the 3% difference, the least repeated the error - so one out of 20 polls may show the NDP at 3% lower or higher, but 10 out of twenty would have them between + /- 1%, and 15 would have them within + /- 2%. The value of the error itself being a statistical distribution.
Moreover, as I indicated, these error figures are "non-distributive", but the effect on the polling is a distributed effect (i.e. the distribution must always total 100% - Thus if a party goes up, somewhere else figures must come down. The statistical likelihood, however, that the NDP be down 3% while only the liberals be up the same 3% is probably in the order of one in a thousand chance (sorry, don't have my tables with me and don't remember the formula by hearth anymore).
/even more pedant off.
:irony: