Year	% of total
1990	18.8697908913483
1995	18.7731209335025
2000	19.3984416636385
2005	18.2414454124097
2010	18.9375155841204
2011	20.3180202081293
2012	18.2417585169195
2013	16.8424494037064
2014	14.3068561073414
2015	13.622246388505
2016	9.22074828793886
2017	9.22071834387081