(Reuters) - A majority of Swiss have voted in a referendum to ease the expulsion of foreigners convicted of serious crimes such as murder, while rejecting a proposal to impose a minimum cantonal (state) tax on the very wealthy.

Referendums are an important part of Switzerland’s tradition of direct democracy. Here are some facts about them:

* WHAT WAS AT ISSUE ON NOV. 28?

-- Most voters backed a measure to expel foreigners found guilty of serious crimes such as murder automatically, as proposed by the right-wing Swiss People’s Party (SVP). Currently deportations are dealt with on a case-by-case basis.

-- Voters rejected a proposal by the center-left Social Democrats to impose a minimum cantonal (provincial) tax on the ultra wealthy. The measure would have stopped cantons attracting the rich by undercutting one another on tax rates, a policy which -- along with competition on corporate taxation -- has helped draw foreign millionaires and multinationals to Switzerland.

* TYPES OF REFERENDUMS

-- In Switzerland, referendums are held at federal, cantonal and municipal level, often several times a year.

-- Voter turnout in recent years has averaged slightly over 40 percent, though some more controversial proposals have won much larger turnouts.

-- Mandatory referendums apply to all amendments to the constitution and proposals for membership of specific international organizations. Such referendums require a double majority, a majority of votes cast plus a majority of cantons.

-- A so-called ‘facultative referendum’ is held on federal laws and certain types of international treaties if at least 50,000 people or eight cantons have petitioned for one within 100 days of the item’s official publication.

-- There are also popular initiatives, which at the federal level need to collect 100,000 valid signatures within 18 months.

-- Authorities often respond with a counter proposal to popular initiatives (generally less far-reaching) in the hope that voters will approve that instead.

-- Since 1987 the possibility of a double “yes” has existed, meaning that voters can approve both the initiative and its counter proposal.

* CONTROVERSIAL VOTES

-- In March 2010, voters rejected a proposal that would have granted legal representation to abused animals.

-- The Swiss voted in November 2009 to ban the construction of new minarets in November 2009. Some 58 percent of voters and all but four of the 26 cantons approved the proposal in the nationwide referendum, which was backed by the SVP.

-- In 2004, 56 percent of voters approved a measure allowing the life-long incarceration of people convicted of serious violent or sexual crimes and deemed not treatable with therapy.

-- In 1992, they voted by a slim margin -- 50.3 to 49.7 percent -- against membership in the European Economic Area.

-- In 1989, 64 percent of voters rejected an initiative called “Switzerland without an Army.”