Year	% of total
1971	26.17258907137473
1972	25.142369922295938
1973	24.825858014960964
1974	24.658988343539136
1975	24.642843245127114
1976	24.159010513428825
1977	24.117832718070808
1978	25.859809377195774
1979	24.828307480932295
1980	23.768962999371105
1981	22.87381418907136
1982	20.931622150157956
1983	19.212242384849166
1984	18.659099553898603
1985	17.35039773991119
1986	17.42803481756349
1987	15.058251761312604
1988	15.880293651576563
1989	15.980127856319351
1990	20.296670762339563
1991	20.41776132548901
1992	20.215997242919823
1993	20.36967498131496
1994	21.353663560652294
1995	19.358712405698448
1996	18.714994595770392
1997	17.904652016287304
1998	18.336133131104283
1999	17.600151937833274
2000	15.874446972182337
2001	15.896882581113903
2002	14.958857414364463
2003	15.781296293952543
2004	15.750712392432106
2005	16.58224175358656
2006	16.70491157231009
2007	16.097663669536715
2008	14.962075859701212
2009	14.348557746975118
2010	14.631227508045761
2011	14.837050373310875
2012	13.968796553025891
2013	14.7442168214264
2014	13.699680445717014
2015	12.632887373272213