Year	% of total
1971	2.0866837321981544
1972	2.064034577895236
1973	2.1581787060741693
1974	2.1955995318178587
1975	2.399046180811358
1976	2.296660496191431
1977	2.3181975268809185
1978	2.198769872343063
1979	2.6366110711488777
1980	2.7791701462326133
1981	2.746574762645902
1982	3.260879223442924
1983	3.0877910020752233
1984	3.1586216112617844
1985	3.4086550024364795
1986	3.3613929113887546
1987	3.919315318378539
1988	4.3879185682383515
1989	4.825069674765533
1990	22.57911517266467
1991	22.09034345986054
1992	21.20431232969849
1993	20.454720878595204
1994	19.172703326064973
1995	18.9094116485964
1996	19.126968390485793
1997	19.469408061890903
1998	19.649320846841466
1999	20.51990436916451
2000	20.522094879088016
2001	21.000262065880047
2002	21.18202737349928
2003	21.72019298313621
2004	21.514489246859835
2005	21.1041034004875
2006	20.402517860614726
2007	20.363049163590045
2008	20.56999043675863
2009	20.38203428112674
2010	20.33063957190422
2011	18.87595634065084
2012	18.620852237083266
2013	17.880409521897153
2014	18.237892886938948
2015	18.493136034095397