Lies, damned lies and opinion polls: some essential background

Explaining disparate results

Several factors may contribute to different poll results. It may be that the pollsters use different calculations to "weight" their samples to reflect the population. Or, one polling organisation may exclude from its calculations the responses of those who do not answer or who say they "don’t know" while another may allocate them according to the respondent’s political "leaning".

Both approaches may create differences between poll results and election results. Discarding the "uncommitted" responses and recomputing the percentages based on definite answers assumes that the undecided will cast their votes as the more committed voters do. Urging "uncommitted" respondents to select a party, or assigning these responses on the basis of party identification or "leaning", assumes that undecided voters will "come home" and vote for that party at an election.

Party identification

A problem with urging those who "don’t know" to nominate a party is the assumption that all voters identify with a party strongly enough to vote for it at an election. However, election specialist Professor Ian McAllister has shown that, although most voters still identify with a party, more now have no party attachment or are less attached to their party than previously. McAllister’s figures show that the number of voters who do not identify with a major party has increased from 5 per cent of respondents in 1987 to 15 per cent of respondents in 2001. In addition, the strength of party identification has declined substantially: in 1979, 34 per cent of respondents had "very strong" identification with their party; in 2001, only 18 per cent had such a strong attachment.

Thus, it cannot be assumed that ‘don’t know’ respondents will vote for the party they lean towards or the party for which they voted previously. Assigning them on this basis could distort poll results vis-àvis election results.

Some additional pitfalls

Other factors that may affect poll results can be discussed in the context of the 2001 pre-election polls. A week before the election, Newspoll had the Coalition at 45 per cent and Labor at 39.5 per cent while Morgan had the Coalition at 38.5 per cent and Labor at 43.5 per cent. Newspoll’s figures were close to the election outcome (Coalition 42.7 per cent; Labor 37.8 per cent). This is not to argue for one pollster over the other.  In fact, a recent academic comparison found that, over the longer term, election betting was a better predictor of election results than opinion polls.

How then can we account for the disparity between polls on the same issue? Ultimately, it is impossible to explain with certainty, although several factors may contribute, including those discussed above.

Other factors, such as different timing of interviews or different question wording, do not help here because both polls asked the same thing at the same time. The polls use different methods to gather data, which may have some effect — Newspoll uses telephone interviews while Morgan uses face-to-face interviews. Those in the polling industry disagree as to how the different techniques affect results, and academics, too, are undecided on this issue.

Morgan’s executive chairman, Gary Morgan, claims that the electorate changed its mind in the last week, and notes that re-interviews after the election showed that 20 per cent had changed their minds in the last days of the campaign. Morgan highlights the Tampa crisis and the September 11 terrorist attacks in the United States as turning points in the fortunes of the Coalition government.  

Election analyst Antony Green had predicted that asylum seekers and security would decide the 2001 election, despite polls showing that health, education and the economy were the top issues in voters’ minds. This suggests that the important poll results were not those on the importance of issues per se, but those on the party preferred to handle those issues at the forefront of the campaign — immigration and defence. On these issues, the Coalition  score higher than Labor.

Thus, the prominence of an issue at the time, as well as the perceived party differential on that issue, may have more effect on how people cast their votes on polling day.

The nation’s pulse

None of the factors mentioned above offers a definitive explanation of the different poll results before the 2001 election. For example, Morgan’s claim that voters changed their minds in the last week does not account for Newspoll’s accuracy a week before the election. In fact, Murray Goot notes that the Newspoll and ACNielsen polls in the last week showed little sign of movement, and concludes that Morgan’s explanation “is not plausible and is not supported by other polls”.

Perhaps the most important point about opinion polls is that polling is not an exact science. In the words of American humorist E. B. White:

The so-called science of poll-taking is not a science at all but a mere necromancy. People are unpredictable by nature, and although you can take a nation’s pulse, you can’t be sure that the nation hasn’t just run up a flight of stairs.