اثر ارابه موسیقی
معمولاً آدمیان هنگامی که متوجه شوند (یا به آنان القا شود) که مردمان بسیار دیگری به اندیشهای معتقدند، احتمال اینکه بدون اندیشه آن را بپذیرند، بسیار افزایش مییابد. به این اثر، اثر ارابه موسیقی (به انگلیسی: Bandwagon effect) گویند و بر پایه آن روشهایی برای پروپاگاندا و سواستفاده بنیان میشود. این اثر که نوعی سوگیری شناختی است که طی آن، فرد عملی را فقط به این دلیل انجام میدهد که دیگران نیز دارند همان کار را میکنند. در این حالت فرد به باورهای خود توجه چندانی ندارد و پس از اینکه عملی را انجام داد به باورهای خویش رجوع میکند. اگر عمل با باورهایش مطابقت داشت ارزش زیادی برای باور خود قائل میشود، اگر با باورش تناقض داشت، باورش را نادیده میگیرد. 
در سال ۱۸۴۸ یکی از نامزدهای ریاست جمهوری آمریکا با استفاده از دلقکی به نام دن رایس، ارابههای موسیقی در شهرها به حرکت در آورد. این نوآوری وی در جذب مخاطب، بسیار مؤثر عمل کرد. موفقیت این ایده باعث شد، سیاستمداران بیشتری راغب شوند که بر روی ارابه موسیقی بنشینند و خود را در طرف موفقیت نشان دهند. رفته رفته تا به سال ۱۹۰۰ استفاده از ارابهموسیقی به یک استاندراد برای تبلیغات ریاستجمهوری در آمریکا در آمد. اکنون استفاده از اصطلاح «ارابه موسیقی» بیشتر برای تحقیر کردن یک روش یا گروه استفاده میشود. مثلاً اصطلاح «پریدن بر روی ارابه موسیقی»، دلالت دارد؛ بر علاقه بدون اندیشه فرد مورد اشاره، به ربط دادن خود به آنچه موفقیت پنداشته میشود،
در رایگیریهای عمومی مواردی دیده شدهاست که رایدهندگان به گروه یا فردی، که حدس زده میشود برنده شود، تمایل پیدا میکنند؛ بدون اندیشه درباره آن گروه یا فرد. با این کار آنان تصور کنند که خود را در «طرف برنده» قرار دادهاند.
بسیار دیده شدهاست که مردمان بسیاری تنها وقتی ترانهای برایشان محبوب است که برای مردمان زیادی آن ترانه محبوب میشود.
در اقتصاد خرد[ویرایش]
در اقتصاد خرد، گاهی این اصطلاح برای توصیف روابط بین «نیاز» و «تقاضا» برای یک محصول به کار برده میشود.  مشاهده شدهاست که علاقه توده مردم به یک محصول هنگامی که فروش آن زیاد گردد، به صورت غیر منطقی افزایش مییابد که این معمولاً با اصول تئوری عرضه و تقاضا منافات دارد. معمولاً فرض میشود که مشتریان کالا با توجه به قیمت و نیاز خود تصمیمگیری میکنند، که این فرض گاهی اوقات به خاطر این اثر یا آثار دیگر، برقرار نمیگردد.
The bandwagon effect is a phenomenon whereby the rate of uptake of beliefs, ideas, fads and trends increases the more that they have already been adopted by others. In other words, the bandwagon effect is characterized by the probability of individual adoption increasing with respect to the proportion who have already done so. As more people come to believe in something, others also "hop on the bandwagon" regardless of the underlying evidence.
The tendency to follow the actions or beliefs of others can occur because individuals directly prefer to conform, or because individuals derive information from others. Both explanations have been used for evidence of conformity in psychological experiments. For example, social pressure has been used to explain Asch's conformity experiments, and information has been used to explain Sherif's autokinetic experiment.
According to this concept, the increasing popularity of a product or phenomenon encourages more people to "get on the bandwagon", too. The bandwagon effect explains why there are fashion trends.
When individuals make rational choices based on the information they receive from others, economists have proposed that information cascades can quickly form in which people decide to ignore their personal information signals and follow the behavior of others. Cascades explain why behavior is fragile—people understand that they are based on very limited information. As a result, fads form easily but are also easily dislodged. Such informational effects have been used to explain political bandwagons.
The definition of a bandwagon is a wagon which carries a band during the course of a parade, circus or other entertainment event. The phrase "jump on the bandwagon" first appeared in American politics in 1848 when Dan Rice, a famous and popular circus clown of the time, used his bandwagon and its music to gain attention for his political campaign appearances. As his campaign became more successful, other politicians strove for a seat on the bandwagon, hoping to be associated with his success. Later, during the time of William Jennings Bryan's 1900 presidential campaign, bandwagons had become standard in campaigns, and the phrase "jump on the bandwagon" was used as a derogatory term, implying that people were associating themselves with success without considering that with which they associated themselves.
The bandwagon effect occurs in voting: some people vote for those candidates or parties who are likely to succeed (or are proclaimed as such by the media), hoping to be on the "winner's side" in the end. The bandwagon effect has been applied to situations involving majority opinion, such as political outcomes, where people alter their opinions to the majority view. Such a shift in opinion can occur because individuals draw inferences from the decisions of others, as in an informational cascade.
Because of time zones, election results are broadcast in the eastern parts of the United States while polls are still open in the west. This difference has led to research on how the behavior of voters in western United States is influenced by news about the decisions of voters in other time zones. In 1980, NBC News declared Ronald Reagan to be the winner of the presidential race on the basis of the exit polls several hours before the voting booths closed in the west.
It is also said to be important in the American presidential primary elections. States all vote at different times, spread over some months, rather than all on one day. Some states (Iowa, New Hampshire) have special precedence to go early while others choose to wait until a certain date. This is often said to give undue influence to these states, a win in these early states is said to give a candidate the "Big Mo" (momentum) and has propelled many candidates to win the nomination. Because of this, other states often try front loading (going as early as possible) to make their say as influential as they can. In the 2008 presidential primaries two states had all or some of their delegates banned from the convention by the central party organizations for voting too early.
Several studies have tested this theory of the bandwagon effect in political decision making. In the 1994 study of Robert K. Goidel and Todd G. Shields in The Journal of Politics, 180 students at the University of Kentucky were randomly assigned to nine groups and were asked questions about the same set of election scenarios. About 70% of subjects received information about the expected winner. Independents, which are those who do not vote based on the endorsement of any party and are ultimately neutral, were influenced strongly in favor of the person expected to win. Expectations played a significant role throughout the study. It was found that independents are twice as likely to vote for the Republican candidate when the Republican is expected to win. From the results, it was also found that when the Democrat was expected to win, independent Republicans and weak Republicans were more likely to vote for the Democratic candidate.
A study by Albert Mehrabian, reported in the Journal of Applied Social Psychology (1998), tested the relative importance of the bandwagon (rally around the winner) effect versus the underdog (empathic support for those trailing) effect. Bogus poll results presented to voters prior to the 1996 Republican primary clearly showed the bandwagon effect to predominate on balance. Indeed, approximately 6% of the variance in the vote was explained in terms of the bogus polls, showing that poll results (whether accurate or inaccurate) can significantly influence election results in closely contested elections. In particular, assuming that one candidate "is an initial favorite by a slim margin, reports of polls showing that candidate as the leader in the race will increase his or her favorable margin". Thus, as poll results are repeatedly reported, the bandwagon effect will tend to snowball and become a powerful aid to leading candidates.
During the 1992 U.S. presidential election, Vicki G. Morwitz and Carol Pluzinski conducted a study, which was published in The Journal of Consumer Research (1996). At a large northeastern university, some of 214 volunteer business students were given the results of student and national polls indicating that Bill Clinton was in the lead. Others were not exposed to the results of the polls. Several students who had intended to vote for Bush changed their minds after seeing the poll results.
Additionally, British polls have shown an increase to public exposure. Sixty-eight percent of voters had heard of the general election campaign results of the opinion poll in 1979. In 1987, this number of voters aware of the results increased to 74%. According to British studies, there is a consistent pattern of apparent bandwagon effects for the leading party.
In a study published in the European Economic Review (2015), Morton and co-authors, used the large number of time zones across French overseas territories, to study the bandwagon effect. Before 2002, all territories were voting on Sunday in the presidential elections. For that reason, voters in territories located to the West of mainland France (e.g. French Guyana) could observe the exit polls from mainland France before the close of their local polling booths. After 2002, a law was passed for these territories to vote on Saturday, in order to avoid this situation. The authors observed a bandwagon effect: when voters from Western territories could observe the winner in mainland France, this candidate was doing much better locally. After 2002, when voting in these territories took place before mainland France, this bandwagon voting disappeared.
In microeconomics, bandwagon effects may play out in interactions of demand and preference.[need quotation to verify] The bandwagon effect arises when people's preference for a commodity increases as the number of people buying it increases. This interaction potentially disturbs the normal results of the theory of supply and demand, which assumes that consumers make buying decisions solely based on price and their own personal preference.
Medical bandwagons have been identified as "the overwhelming acceptance of unproved but popular ideas". They have led to inappropriate therapies for numerous patients, and have impeded the development of more appropriate treatment.
In Lawrence Cohen and Henry Rothschild's exposition The Bandwagons of Medicine (1979) several of these therapeutic misadventures, some of which persisted for centuries before they were abandoned, substituted by another bandwagon, or replaced by a scientifically valid alternative. The ancient serpent cult of Aesculapius, in which sacred snakes licked the afflicted as treatment of their diseases, is an example of a bandwagon gathering momentum based on a strong personality, in this case a Roman god.
One who supports a particular sports team, despite having shown no interest in that team until it started gaining success, can be considered a "bandwagon fan". One recent example in the United States is the Golden State Warriors, who rose to prominence by winning the 2015 NBA Finals, followed by a record-breaking 73-9 record the following year. Consequently, sales of point guard Stephen Curry's jersey skyrocketed. Curry merchandise sales in the first two weeks of the 2015–2016 season were 453% higher than in the first two weeks of the 2014–2015 season, including a 581% increase in sales of his jersey; his merchandise was a top-seller in 38 of the 50 U.S. states, and the Warriors' merchandise became the best-selling of any NBA team.