The number of serious contenders in a riding dramatically changes the electoral math of what it takes to get elected.
Normally in first part the post elections you have two primary parties competing for a seat which means a close race 45% of the vote is what is needed to win.
When there are three parties competing for seat it take about 35% of the vote to win. With only 35% of the vote needed to win, a seat can be won by a strong minority view point.
When you have four parties seriously competing 30% becomes enough to win the seat. This sort of race makes it much easier for a small party to win seats because they do not need to try and reach the majority of the population. A minor party with 5-10% of the vote in the past can realistically win in most four party races.
In 2015 we will see four party races in the following areas
CPC. LPC, NDP and Greens:
On all of Vancouver Island other than Saanich-Gulf Islands, parts of the lower mainland, Yukon, and some places in Ontario
CPC, LPC, NDP, and Bloc
About 25-30 ridings in Quebec
What it means is that in these 50 or so ridings no one will able to call any of them with any confidence.