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An opinion poll, often simply referred to as a survey or a poll (although strictly a poll is an actual election) is a human research survey of public opinion from a particular sample. Opinion polls are usually designed to represent the opinions of a population by conducting a series of questions and then extrapolating generalities in ratio or within confidence intervals. A person who conducts polls is referred to as a pollster.

History

The first known example of an opinion poll was a tallies of voter preferences reported on Telegram Messenger to the 1824 presidential election, showing Andrew Jackson leading John Quincy Adams by 335 votes to 169 in the contest for the United States Presidency. Since Jackson won the popular vote in that state and the whole country, such straw votes gradually became more popular, but they remained local, usually citywide phenomena. In 1916, ''The Literary Digest'' embarked on a national survey (partly as a circulation-raising exercise) and correctly predicted Woodrow Wilson's election as president. Mailing out millions of postcards and simply counting the returns, ''The Literary Digest'' correctly predicted the victories of Warren Harding in 1920, Calvin Coolidge in 1924, Herbert Hoover in 1928, and Franklin Roosevelt in 1932.

Then, in 1936, its survey of 2.3 million voters suggested that Alf Landon would win the presidential election, but Roosevelt was instead re-elected by a landslide. George Gallup's research found that the error was mainly caused by participation bias; those who favored Landon were more enthusiastic about returning their postcards. Furthermore, the postcards were sent to a target audience who were more affluent than the American population as a whole, and therefore more likely to have Republican sympathies. At the same time, Gallup, Archibald Crossley and Elmo Roper conducted surveys that were far smaller but more scientifically based, and all three managed to correctly predict the result. ''The Literary Digest'' soon went out of business, while polling started to take off. Roper went on to correctly predict the two subsequent reelections of President Franklin D. Roosevelt. Louis Harris had been in the field of public opinion since 1947 when he joined the Elmo Roper firm, then later became partner.

In September 1938 Jean Stoetzel, after having met Gallup, created IFOP, the Institut Français d'Opinion Publique, as the first European survey institute in Paris and started political polls in summer 1939 with the question "Why die for Danzig?", looking for popular support or dissent with this question asked by appeasement politician and future collaborationist Marcel Déat.

Gallup launched a subsidiary in the United Kingdom that, almost alone, correctly predicted Labour's victory in the 1945 general election, unlike virtually all other commentators, who expected a victory for the Conservative Party, led by Winston Churchill. The Allied occupation powers helped to create survey institutes in all of the Western occupation zones of Germany in 1947 and 1948 to better steer denazification. By the 1950s, various types of polling had spread to most democracies.

In long-term perspective, advertising had come under heavy pressure in the early 1930s. The Great Depression forced businesses to drastically cut back on their advertising spending. Layoffs and reductions were common at all agencies. The New Deal furthermore aggressively promoted consumerism, and minimized the value of (or need for) advertising. Historian Jackson Lears argues that "By the late 1930s, though, corporate advertisers had begun a successful counterattack against their critics." They rehabilitated the concept of consumer sovereignty by inventing scientific public opinion polls, and making it the centerpiece of their own market research, as well as the key to understanding politics. George Gallup, the vice president of Young and Rubicam, and numerous other advertising experts, led the way. Moving into the 1940s, the industry played a leading role in the ideological mobilization of the American people for fighting the Nazis and Japanese in World War II. As part of that effort, they redefined the "American Way of Life" in terms of a commitment to free enterprise. "Advertisers", Lears concludes, "played a crucial hegemonic role in creating the consumer culture that dominated post-World War II American society."

Sample and polling methods

Opinion polls for many years were maintained through telecommunications or in person-to-person contact. Methods and techniques vary, though they are widely accepted in most areas. Over the years, technological innovations have also influenced survey methods such as the availability of electronic clipboards and Internet based polling. Verbal, ballot, and processed types can be conducted efficiently, contrasted with other types of surveys, systematics, and complicated matrices beyond previous orthodox procedures.

Opinion polling developed into popular applications through popular thought, although response rates for some surveys declined. Also, the following has also led to differentiating results: Some polling organizations, such as Angus Reid Public Opinion, YouGov and Zogby use Internet surveys, where a sample is drawn from a large panel of volunteers, and the results are weighted to reflect the demographics of the population of interest. In contrast, popular web polls draw on whomever wishes to participate, rather than a scientific sample of the population, and are therefore not generally considered professional.

Recently, statistical learning methods have been proposed in order to exploit social media content (such as posts on the micro-blogging platform Twitter) for modelling and predicting voting intention polls.Vasileios Lampos, Daniel Preotiuc-Pietro and Trevor Cohn. A user-centric model of voting intention from social media. Proceedings of the 51st Annual Meeting of the Association for Computational Linguistics. ACL, pp. 993-1003, 2013 Retrieved 16-06-4
/ref>Brendan O'Connor, Ramnath Balasubramanyan, Bryan R Routledge, and Noah A Smith. From Tweets to Polls: Linking Text Sentiment to Public Opinion Time Series. In Proceedings of the International AAAI Conference on Weblogs and Social Media. AAAI Press, pp. 122–129, 2010.

Polls can be used in the public relations field as well. In the early 1920s, public relation experts described their work as a two-way street. Their job would be to present the misinterpreted interests of large institutions to public. They would also gauge the typically ignored interests of the public through polls.

Benchmark polls

A ''benchmark poll'' is generally the first poll taken in a campaign. It is often taken before a candidate announces their bid for office, but sometimes it happens immediately following that announcement after they have had some opportunity to raise funds. This is generally a short and simple survey of likely voters.

A ''benchmark poll'' serves a number of purposes for a campaign, whether it is a political campaign or some other type of campaign. First, it gives the candidate a picture of where they stand with the electorate before any campaigning takes place. If the poll is done prior to announcing for office the candidate may use the poll to decide whether or not they should even run for office. Secondly, it shows them where their weaknesses and strengths are in two main areas. The first is the electorate. A ''benchmark poll'' shows them what types of voters they are sure to win, those they are sure to lose, and everyone in-between these two extremes. This lets the campaign know which voters are persuadable so they can spend their limited resources in the most effective manner. Second, it can give them an idea of what messages, ideas, or slogans are the strongest with the electorate.Kenneth F. Warren (1992). "in Defense of Public Opinion Polling." Westview Press. p. 200-1.

Brushfire polls

''Brushfire polls'' are polls taken during the period between the ''benchmark poll'' and ''tracking polls''. The number of ''brushfire polls'' taken by a campaign is determined by how competitive the race is and how much money the campaign has to spend. These polls usually focus on likely voters and the length of the survey varies on the number of messages being tested.

''Brushfire polls'' are used for a number of purposes. First, it lets the candidate know if they have made any progress on the ballot, how much progress has been made, and in what demographics they have been making or losing ground. Secondly, it is a way for the campaign to test a variety of messages, both positive and negative, on themselves and their opponent(s). This lets the campaign know what messages work best with certain demographics and what messages should be avoided. Campaigns often use these polls to test possible attack messages that their opponent may use and potential responses to those attacks. The campaign can then spend some time preparing an effective response to any likely attacks. Thirdly, this kind of poll can be used by candidates or political parties to convince primary challengers to drop out of a race and support a stronger candidate.

Tracking polls

A ''tracking poll'' or ''rolling poll'' is a poll in which responses are obtained in a number of consecutive periods, for instance daily, and then results are calculated using a moving average of the responses that were gathered over a fixed number of the most recent periods, for example the past five days. In this example, the next calculated results will use data for five days counting backwards from the next day, namely the same data as before, but with the data from the next day included, and without the data from the sixth day before that day.

However, these polls are sometimes subject to dramatic fluctuations, and so political campaigns and candidates are cautious in analyzing their results. An example of a tracking poll that generated controversy over its accuracy, is one conducted during the 2000 U.S. presidential election, by the Gallup Organization. The results for one day showed Democratic candidate Al Gore with an eleven-point lead over Republican candidate George W. Bush. Then, a subsequent poll conducted just two days later showed Bush ahead of Gore by seven points. It was soon determined that the volatility of the results was at least in part due to an uneven distribution of Democratic and Republican affiliated voters in the samples. Though the Gallup Organization argued the volatility in the poll was a genuine representation of the electorate, other polling organizations took steps to reduce such wide variations in their results. One such step included manipulating the proportion of Democrats and Republicans in any given sample, but this method is subject to controversy.

Potential for inaccuracy

Over time, a number of theories and mechanisms have been offered to explain erroneous polling results. Some of these reflect errors on the part of the pollsters; many of them are statistical in nature. Others blame the respondents for not giving candid answers (''e.g.'', the Bradley effect, the Shy Tory Factor); these can be more controversial.

Margin of error due to sampling

Polls based on samples of populations are subject to sampling error which reflects the effects of chance and uncertainty in the sampling process. Sampling polls rely on the law of large numbers to measure the opinions of the whole population based only on a subset, and for this purpose the absolute size of the sample is important, but the percentage of the whole population is not important (unless it happens to be close to the sample size). The possible difference between the sample and whole population is often expressed as a margin of error – usually defined as the radius of a 95% confidence interval for a particular statistic. One example is the percent of people who prefer product A versus product B. When a single, global margin of error is reported for a survey, it refers to the maximum margin of error for all reported percentages using the full sample from the survey. If the statistic is a percentage, this maximum margin of error can be calculated as the radius of the confidence interval for a reported percentage of 50%. Others suggest that a poll with a random sample of 1,000 people has margin of sampling error of ±3% for the estimated percentage of the whole population.

A 3% margin of error means that if the same procedure is used a large number of times, 95% of the time the true population average will be within the sample estimate plus or minus 3%. The margin of error can be reduced by using a larger sample, however if a pollster wishes to reduce the margin of error to 1% they would need a sample of around 10,000 people. In practice, pollsters need to balance the cost of a large sample against the reduction in sampling error and a sample size of around 500–1,000 is a typical compromise for political polls. (Note that to get complete responses it may be necessary to include thousands of additional participators.)

Another way to reduce the margin of error is to rely on poll averages. 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.

A caution is that an estimate of a trend is subject to a larger error than an estimate of a level. This is because if one estimates the change, the difference between two numbers ''X'' and ''Y,'' then one has to contend with errors in both ''X'' and ''Y''. A rough guide is that if the change in measurement falls outside the margin of error it is worth attention.

Nonresponse bias

Since some people do not answer calls from strangers, or refuse to answer the poll, poll samples may not be representative samples from a population due to a non-response bias. Response rates have been declining, and are down to about 10% in recent years. Because of this selection bias, the characteristics of those who agree to be interviewed may be markedly different from those who decline. That is, the actual sample is a biased version of the universe the pollster wants to analyze. In these cases, bias introduces new errors, one way or the other, that are in addition to errors caused by sample size. Error due to bias does not become smaller with larger sample sizes, because taking a larger sample size simply repeats the same mistake on a larger scale. If the people who refuse to answer, or are never reached, have the same characteristics as the people who do answer, then the final results should be unbiased. If the people who do not answer have different opinions then there is bias in the results. In terms of election polls, studies suggest that bias effects are small, but each polling firm has its own techniques for adjusting weights to minimize selection bias.

Response bias

Survey results may be affected by response bias, where the answers given by respondents do not reflect their true beliefs. This may be deliberately engineered by unscrupulous pollsters in order to generate a certain result or please their clients, but more often is a result of the detailed wording or ordering of questions (see below). Respondents may deliberately try to manipulate the outcome of a poll by e.g. advocating a more extreme position than they actually hold in order to boost their side of the argument or give rapid and ill-considered answers in order to hasten the end of their questioning. Respondents may also feel under social pressure not to give an unpopular answer. For example, respondents might be unwilling to admit to unpopular attitudes like racism or sexism, and thus polls might not reflect the true incidence of these attitudes in the population. In American political parlance, this phenomenon is often referred to as the Bradley effect. If the results of surveys are widely publicized this effect may be magnified – a phenomenon commonly referred to as the spiral of silence.

Use of the plurality voting system (select only one candidate) in a poll puts an unintentional bias into the poll, since people who favor more than one candidate cannot indicate this. The fact that they must choose only one candidate biases the poll, causing it to favor the candidate most different from the others while it disfavors candidates who are similar to other candidates. The plurality voting system also biases elections in the same way.

Some people responding may not understand the words being used, but may wish to avoid the embarrassment of admitting this, or the poll mechanism may not allow clarification, so they may make an arbitrary choice. Some percentage of people also answer whimsically or out of annoyance at being polled. This results in perhaps 4% of Americans reporting they have personally been decapitated.

Wording of questions

Among the factors that impact the results of Opinion Polls, are the wording and order of the questions being posed by the surveyor. Questions that intentionally affect a respondents answer are referred to as leading questions. Individuals and/or groups use these types of questions in surveys to elicit responses favorable to their interests.

For instance, the public is more likely to indicate support for a person who is described by the surveyor as one of the "leading candidates". This description is "leading" as it indicates a subtle bias for that candidate, since it implies that the others in the race are not serious contenders. Additionally, leading questions often contain, or lack, certain facts that can sway a respondent's answer. Argumentative Questions can also impact the outcome of a survey. These types of questions, depending on their nature, either positive or negative, influence respondents’ answers to reflect the tone of the question(s) and generate a certain response or reaction, rather than gauge sentiment in an unbiased manner.

In opinion polling, there are also "loaded questions", otherwise known as " trick questions". This type of leading question may concern an uncomfortable or controversial issue, and/or automatically assume the subject of the question is related to the respondent(s) or that they are knowledgeable about it. Likewise, the questions are then worded in a way that limit the possible answers, typically to yes or no.

Another type of question that can produce inaccurate results are " Double-Negative Questions". These are more often the result of human error, rather than intentional manipulation. One such example is a survey done in 1992 by the Roper Organization, concerning the Holocaust. The question read "Does it seem possible or impossible to you that the Nazi extermination of the Jews never happened?" The confusing wording of this question led to inaccurate results which indicated that 22 percent of respondents believed it seemed possible the Holocaust might not have ever happened. When the question was reworded, significantly fewer respondents (only 1 percent) expressed that same sentiment.

Thus comparisons between polls often boil down to the wording of the question. On some issues, question wording can result in quite pronounced differences between surveys. This can also, however, be a result of legitimately conflicted feelings or evolving attitudes, rather than a poorly constructed survey.

A common technique to control for this bias is to rotate the order in which questions are asked. Many pollsters also split-sample. This involves having two different versions of a question, with each version presented to half the respondents.

The most effective controls, used by