A bellwether is any entity in a given arena that serves to create or influence trends or to presage future happenings.

The term is derived from the Middle English bellewether and refers to the practice of placing a bell around the neck of a castrated ram (a wether) leading its flock of sheep. The movements of the flock could be perceived by hearing the bell before the flock was in sight.

In sociology, the term is applied in the active sense to a person or group of people who tend to create, influence or set trends.

In politics, the term is more often applied in the passive sense to describe a geographic region where political tendencies match in microcosm those of a wider area, such that the result of an election in the former region might predict the eventual result in the latter. In a Westminster-style election, for example, a constituency, the control of which tends frequently to change, can mirror in its popular vote the result on a national scale.

• In the United Kingdom, the Basildon constituency has reflected the overall result in every General Election since its creation in 1974. In addition, Bristol North West is also considered a bellwether: voters usually vote for the winning national party.

• In Australian federal elections, the electoral divisions of Eden-Monaro in New South Wales and Leichhardt in Queensland have elected Members of Parliament from the party which won government at every federal election since 1972. The electoral division of Macarthur in New South Wales was a bellwether from the 1949 election until 2004. However, at the 2007 election Macarthur stayed as a Liberal seat despite a change of government, with sitting MP Pat Farmer narrowly surviving a 11% swing against him. The state of New South Wales could also be considered a bellwether, as the party which wins government has won the majority of House of Representatives seats in that state at every election since 1963. Unlike many bellwethers, these are cited by analysts solely for their record and are not usually attributed demographic factors that reflect the median of Australia.

• In Canada, Sarnia-Lambton has voted for the winning party in every single federal election since it was created in 1968.
  • In Ontario, Peterborough has been won by the party who has won the most seats overall in provincial elections since 1977.

• In the United States, Missouri, often referred to as the Missouri bellwether, has produced the same outcome as the national results in every presidential election beginning in 1904, except in 1956. The American bellwether states are http://unfutz.blogspot.com/2007/02/bellwether-states.html:
  • Missouri - 1 miss (1956) from 1904 on (96.3%), perfect since 1960
  • Tennessee - 1 miss (1960) from 1928 on (95.2%), perfect since 1964
  • Nevada - 1 miss (1976) from 1912 on (88.8%), perfect since 1980
  • Ohio - 2 misses (1944, 1960) from 1896 on (93.1%), perfect since 1964
  • New Mexico - 2 misses (1976, 2000) from 1912 on (92%), perfect from 1912 to 1976
  • Kentucky - 2 misses (1952, 1960) from 1924 on (90.9%), perfect since 1964
  • Delaware - 2 misses (2000, 2004) from 1952 on (86.7%), perfect from 1952 to 1996

In the stock market, a bellwether (barometer stock in the UK) is the stock of a company that is regarded as a leader in its given industry. The performance of the stock is said to reflect the performance of the industry in general. These stocks are used as barometers for the rest of the market. General Motors is an example of a bellwether stock. As the major auto maker in the US, it sets the tone for the rest of the industry. General Motors also has contracts with companies in other industries so its performance is reflected in other sectors of the market.

Trends in expenditure in the UK advertising and marketing industry are monitored in the quarterly Bellwether Report, published by the Institute of Practitioners in Advertising (IPA).

See also

• As Maine goes, so goes the nation
• Missouri bellwether
• Swing state