Year	% of total
1971	19.034859422824262
1972	19.20740829654945
1973	19.3569163766984
1974	20.30307654946088
1975	19.806592426402847
1976	20.13206702724557
1977	20.121271260766243
1978	19.589797896788557
1979	19.728111217533353
1980	19.75428554820081
1981	19.98420442175249
1982	19.67740083943465
1983	19.289199321754953
1984	19.107377001202877
1985	18.720225276415672
1986	18.33795105189479
1987	17.58241713887608
1988	17.861833995749265
1989	17.46703978678519
1990	23.562715817063022
1991	23.563709002773013
1992	23.685895351541784
1993	24.741045541211346
1994	25.433227325125053
1995	25.35552711769261
1996	24.503554642313
1997	24.101054611310015
1998	24.438476338405955
1999	23.616627368329944
2000	22.884322061350133
2001	22.560026939935316
2002	21.878543057219165
2003	20.811036212666195
2004	21.374147087212346
2005	21.308640448619258
2006	20.84633839551541
2007	20.041969237531085
2008	20.189878929154357
2009	20.110799332520823
2010	20.154883542547264
2011	19.094081703152472
2012	19.69190154940125
2013	19.418419280534113
2014	19.50147572365094
2015	19.273090514856666