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Today the Express enthusiastically reported that the UK Independence Party was "poised to be the main opposition party" after a YouGov poll put Ukip at 28%.

The problem with this finding is that it's simply not true.

The paper added that "while other surveys yesterday had Labour just ahead of or level with the Tories, the poll will deepen gloom among Mr. Miliband's MPs".

The reason other papers reported a different ranking is because they selected the correct YouGov findings, while the Express didn't.

The Express took a selective sample of Sun readers from a YouGov survey that actually reported very different findings.

If the Mirror had done the same, for example, Labour would be a certain winner at the general elections.

A little thing called "sampling bias"

If I stood up right now and asked the entire Mirror workforce what the best newspaper in the world is, they'll be much more likely to say it's the Daily Mirror rather than, say, if I asked those who work for the Express. And yet the sample would be quite large given that both papers employ hundreds of people.

But the sample chosen (i.e. the Mirror staffers vs the Express staffers) would not be representative of the entire population. It would be biased.

Sampling bias prejudices our evaluation of the findings.

That's why expert statisticians at YouGov and other organisations take pains to select a sample that is representative of the whole population, which give us more accurate and fair findings.

[Source: YouGov and The Express]