TORONTO—Political public opinion polls remind me of the train schedules in Italy a few decades ago. Even if you couldn't count on the trains to arrive and depart on time, the schedules were very useful for calculating delays. They were an honest guess.

The same goes with political polls. They are very useful if you read them in the context of the last few months' results to try to understand the trends.

With this in mind, the last poll of Ekos for CBC is very informative, mainly for the NDP.

If you look at the results over the last four months, you clearly see the support for the NDP is closely connected to support for the Liberals. When the support for the Grits goes up, the numbers for the NDP go down and vice versa.

Putting aside the support of a certain number of voters who vote for their own political party, no matter the news of the day, all others are up for grabs and the news of the day is very important.

There are no specific numbers, but looking at past electoral results, and excluding Quebec where the dynamic is different, the core support for the Conservatives varies from 20 per cent to 24 per cent, while the Liberal support is a bit higher, but more volatile, and varies between 24 to 28 per cent. The NDP fluctuates between eight to 10 per cent and the Green Party between four to six per cent. The numbers of those who most likely will not change political affiliation in every election fluctuate around 56 per cent to 68 per cent.

That leaves a total of 32 per cent to 44 per cent of people whose vote is up for grabs.

Considering that in the 2008 election, 13,929,093 out of 23,677,639 voters actually cast ballots (58.8 per cent), it means that the number of voters that will help to decide who is going to win or lose an election varies between four and six million. Of course, this will go up or down according to the percentage of voter turnout on election day.

The ability of political parties to win is closely tied to their ability to identify and win the support of those people.

People who belong to this group can be divided in two parts: the most consistent is fluctuating between the Conservatives and the Liberals, the other between the Liberals and the NDP. There is also a wild card involving the Green Party, which receives support mainly from the second group, but also from the centre-right voters.

Of course the Liberal Party can win support from both sides but, at the same time, lose on both.

These considerations are not based on any scientific polls, but are the result of thorough examinations of past election results and some new polls.

Back to last week's poll by Ekos for the CBC.

After the Liberals decided to withdraw support from the minority Conservative government, there was a shift of preferences in the two undecided groups. A number of potential Liberal voters moved towards the Conservatives who increased their support from 35.1 per cent to 37 per cent.

Those are votes that the Conservatives took directly from the Liberals.

Nonetheless, the support for Michael Ignatieff's party remained unchanged for an obvious reason: the centre-left undecided that during the summer parked their vote with the NDP moved to the Liberals to try to stop the Conservatives. In fact, the Liberal support remained unchanged, 29.9 per cent, as unchanged was the support for the Green Party and the Bloc Québécois, while support for the NDP, went down from 16.5 per cent to 13.8 per cent.

This confirms what I wrote last week: in a fight between Harper and Ignatieff, Layton loses if he doesn't choose his targets well or, most of all, decides the role the NDP wants to play in the House of Commons.

Angelo Persichilli is political editor of Corriere Canadese, Canada's Italian-language daily newspaper based in Toronto.

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