POLLING - What is it, and how does it work? 1

This means that 19 out of 20 times, the The third factor that affects the margin of error is how dispersed the data is, or figure in the opinion poll should be within 3% of the ‘true’ figure - the standard deviation. [...] a result, the responses of the sample are more likely to But this does mean that any claims that public attitudes have changed should be closer to the population’s responses, which reduces be based on comparing the results of two or more polls that have asked the the margin of error. [...] We can also adjust for the differences in the places voting each year to pollsters have to make a bunch of choices designed to help them produce estimates of how the parties would have performed if everyone in the gather a representative sample of the voters who would turn up on country had voted – what the BBC calls ‘projected national shares’. [...] Estimating the result requires correctly predicting who estimate how the behaviour of voters in each of these polling stations will win each of these local contests, taking place in a diverse range has changed from one election to the next and examine how the of communities with different circumstances, mixes of voters, patterns of change vary from one seat to the next. [...] However, since weighting is based on the responses in the sample, it can produce distortion in the data if the size of the subgroup in the sample is small, making the results unreliable.