A primary election is an election that narrows the field of candidates before an election for office. Primary elections are one means by which a political party or a political alliance nominates candidates for an upcoming general election or by-election. Primaries are common in the United States, where their origins are traced to the progressive movement to take the power of candidate nomination from party leaders to the people. Other methods of selecting candidates include caucuses, conventions, and nomination meetings. Historically, Canadian political parties chose their candidates through nominating conventions held by constituency riding associations. Canadian party leaders are elected at leadership conventions, although some parties have abandoned this practice in favor of one member, one vote systems.