Year	% of total
1971	26.80483128349088
1972	26.680122182496333
1973	25.11204696261559
1974	24.21935106522851
1975	25.576429046409643
1976	26.876293081186592
1977	27.2472005299328
1978	28.422858496706272
1979	29.74713900766752
1980	30.50814433516509
1981	33.006618267006104
1982	32.545254647806885
1983	32.9178281733479
1984	36.54192669620627
1985	37.12860810966223
1986	37.21537360731855
1987	37.32050112021067
1988	37.45203401530916
1989	37.6739201470217
1990	43.11082059069998
1991	45.56752368983007
1992	49.511150398950484
1993	55.27552598893023
1994	54.92971359619986
1995	54.82541433694639
1996	55.56844189814909
1997	56.124235824146275
1998	57.6909431333251
1999	57.304896357183786
2000	57.10670033660161
2001	57.92376498546686
2002	58.375204199549366
2003	57.88492081335481
2004	58.42926297363109
2005	61.673261573913315
2006	63.0846042249689
2007	60.9607487886174
2008	60.27799856255419
2009	61.15584993698992
2010	60.13670454112384
2011	61.75950585879898
2012	62.8414133047551
2013	61.61653330436238
2014	64.13150587251052
2015	65.67928768973526