But pandering to public opinion and leading public opinion do not exhaust the ways in which political leaders and citizens interact. Politicians can be sensitive to underlying public values while leaning against current public preferences. In response to public concerns, they can, as Bush did by going to Congress and to the UN Security Council for authorization to move against Iraq, adjust the process without changing the content of their policy decisions. Politicians and interest group leaders can also shape—and manipulate—public opinion to build broad nominal support for policies mainly serving the interests of their core supporters. This natural dynamic of politics has, in the era of the permanent campaign, dramatically increased the artificiality and disingenuousness of much public discourse. Thats why we have polls about politics.

However, their main use is prior to elections, where politicians use polls as a tool to inform their campaigns and to craft messaging. As such, they are not independent of the political process, Professor Kuha says.

Rather, they could also influence voters’ behaviour by affecting expectation about the outcomes of the election.

People tend to respond to polls in a predictable manner.

Another way to reduce the margin of error is to rely on poll averages, polls about politics. This makes the assumption that the procedure is similar enough between many different polls and uses the sample size of each poll to create a polling average. Another source of error stems from faulty demographic models by pollsters who weigh their samples by particular variables such as party identification in an election. For example, if you assume that the breakdown of the US population by party identification has not changed since the previous presidential election, you may underestimate a victory or a defeat of a particular party candidate that saw a surge or decline in its party registration relative to the previous presidential election cycle.

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.

Polls can be used to measure public opinion.

Opinion polls, he explains, are a survey of public opinion from a particular sample group, and as such can be useful in informing politicians about the views of specific groups of people. In practice, pollsters need to balance the cost of polling a large sample against the reduction in sampling error, and so a typical compromise for political pollsters is to use a sample size of 1,000-10,000 respondents.

Whether the public is actually swayed by the results of opinion polls is hard to say. One test is provided by the election polls. If opinion surveys exert an important influence on the public, then the division of opinion during an election campaign should be in the same direction as the polling results. The leading candidate should gain in strength as the campaign proceeds. Voters who hadn’t made up their minds or who had favored the opposing candidate should be found climbing on the leading candidate’s bandwagon. Can we find any evidence that there is such a trend?