Year	% of total
1971	18.32961990364022
1972	18.55185337260423
1973	19.82101937151098
1974	20.35236508023246
1975	20.994568200601403
1976	21.706612715104953
1977	22.978258853418556
1978	23.78680990773471
1979	24.655808587392258
1980	25.92081876396941
1981	27.337346352995556
1982	28.51413685129034
1983	28.888830362373092
1984	27.93863065994697
1985	28.85576098693004
1986	28.62144846759721
1987	30.742913613485733
1988	31.085399271232518
1989	31.96188186238236
1990	49.18669901586925
1991	49.670013512562456
1992	49.097113718209535
1993	49.28574838760036
1994	47.718488061295965
1995	46.69969263010156
1996	47.21953202548536
1997	47.16287851892874
1998	47.57047025163907
1999	48.254537635606546
2000	47.896237498891445
2001	47.775325492254495
2002	47.5647669974308
2003	47.157684453426896
2004	46.977060268615205
2005	46.2382692537474
2006	45.976954439276945
2007	45.7837176073813
2008	45.697410858396196
2009	43.770657410241824
2010	43.46766321145516
2011	43.92755369662724
2012	43.394865187105445
2013	42.29595784359749
2014	34.38481098002235