"The clubs have attracted the support of opposing factions in the political difficulties of Northern Ireland, which intensified the rivalry in Scotland." Anti-sectarian charity Nil by Mouth notes that some supporters use songs, chants and banners on match days to express abuse or support towards the Protestant or Catholic faiths and proclaim support for Northern Irish-based terrorist groups such as the IRA and UVF. A study in 2008 by the University of Strathclyde found that the Old Firm rivalry was "strongly linked to the conflict in Northern Ireland".