Year	% of total
1971	15.039274818143172
1972	17.29707101667045
1973	21.0587295326368
1974	22.26979092274106
1975	23.061829073327168
1976	25.743226676259972
1977	25.856454169908787
1978	26.42065483061296
1979	30.385145546760246
1980	36.52142473900557
1981	35.24437241149893
1982	35.46385217131714
1983	33.690279054805146
1984	36.13913603830543
1985	36.18528333404148
1986	36.30016669210148
1987	38.98780371911784
1988	39.90183039342161
1989	42.22538587002438
1990	45.80100468493325
1991	45.13065514079434
1992	45.86686175778362
1993	48.98002565537024
1994	50.28741354413327
1995	49.613722872878824
1996	50.12557139848558
1997	50.32029302058854
1998	50.51074735071117
1999	51.97587457870028
2000	52.451912432387225
2001	55.29153153778476
2002	56.05315432602247
2003	57.68417489839105
2004	59.16453361882807
2005	60.861280740476886
2006	61.07451017847977
2007	61.16425764683353
2008	63.32827662346627
2009	63.0052421749456
2010	63.675861471013064
2011	61.70108906247612
2012	60.591764150530835
2013	61.86987132777837
2014	63.366666117482055
2015	66.99069031233496