Over the past eight years support for equal marriage has grown in all 50 US states by an average of 13.6%, a new poll has found.

The poll was published by the UCLA’s Williams Institute, and was titled Public Support for Marriage for Same-Sex Couples by State.

It looked at each state individually and examined their stance on the legal issue of same-sex marriage, as well as considering the overall change in public opinion since 2004.

Over the eight years, all US states have increased in its support for equal marriage, with the average increase being 13.6%. Thirteen states are within 5% of having a majority in favour of equal marriage.

By the end of 2012, 12 states and the District of Columbia had support for equal marriage at or above 50%. Of these 12 states, all currently perform marriages, civil unions, or domestic partnerships for same-sex couples.

Projecting forward, if these trends continue, eight more US states will have over 50% support for marriage equality by the end of 2014.

The poll’s researchers, however, pointed towards a “notable disparity” between states, a press release from the Wiliams Institute said.

Earlier in March, a survey conducted in the US revealed support for same-sex marriage had grown overall to be a “mirror image” of ten years ago, with the majority now in favour of legalisation and many calling for a nationwide law.

The poll found that 58% of Americans now support the legalisation of same-sex marriage, while 36% oppose it.

A new poll by an anti-LGBT rights Christian campaign group LifeWay, in March found that a clear majority of Americans, particularly younger people, support gay rights.

A Pew Research Center poll was released last year, which suggested that there has been a new, and rapid shift in support of equal marriage in the US, except in some southern states.

The Supreme Court Justices two weeks ago indicated a possible interest in striking down the Defense of Marriage Act (DOMA), as it heard arguments around the issue.

This was the second day of hearings, as Tuesday the court heard arguments around Proposition 8, the state of California’s ban on equal marriage. Then the justices questioned the meaning of marriage, and challenged arguments for the ban. 

A decision by the Supreme Court in both cases is expected by the end of June.