photos.com

There are a number of sources of error, the most important one being sampling error. No matter how perfectly a poll is conducted, there will always be a degree of error associated when sampling a small portion of a large population. This is reported as the ‘margin of error’, and in a standard poll of 1,000 people that margin of error is plus or minus 3.1 per cent, 19 times out of 20. That means that if the poll had been conducted in exactly the same way 20 times, in 19 of those cases the results would be within 3.1 points of actual public opinion.

This assumes, however, that the sample was drawn randomly and that everyone in the target population has an equal chance of being interviewed. This is why telephone polling can still carry a margin of error – virtually everyone has a telephone, be it a landline or mobile phone (and yes, most pollsters do sample cell phones). But not everyone will respond. Response rates have dropped to 10 per cent or less, from roughly 1-in-3 in the past. This might have an important effect on the accuracy of a poll, though there is some debate in the industry about whether or not this effect is significant.

Internet polls, as they survey a subset of the population that is a member of a panel, are not supposed to carry margins of error, at least according to the main industry bodies in Canada and the United States. There are still errors associated with these polls, however, but they are not supposed to be measured in the same way as a randomized telephone poll. Nevertheless, internet polls are designed to be as accurate as their telephone counterparts, so should be expected to perform as well. And they usually do.