If the official polls favour Labor, why do the online polls favour the Coalition?

The Nielsen and Morgan polls of late have generally been in favour of Labor…not by much, but by enough. The few online polls that I found today do not seem to represent this trend though, which I find quite interesting. The online polls are all in favour of the Coalition by a large margin.

First up, there’s this one on the Yahoo7 website ^[1]:

62% to 28% favouring the Coalition, with a sample size of 1,500

Then the daily Sky News poll ^[2]:
^[3]
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67% to 33% favouring the Coalition. Sample size unknown.

And the daily NineMSN poll ^[4], directly under the headline of Tony Abbott’s announcement to slash the national immigration intake. The question, whilst not the same as the other two polls, has the same relevance and implications given the policies of the two parties.
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82% to 18% favouring the Coalition’s immigration policy. Sample size 64,021.

So if the big polling companies, with smaller sample sizes, are showing a much closer margin in favour of Labor, is it time for us to start asking questions about the sampling methods of the polling companies?

Samuel