Year	Percent
1970	12.14405
1971	14.39871
1972	16.92555
1973	15.34401
1974	9.6043
1975	7.29375
1976	13.73487
1977	25.47886
1978	35.79273
1979	43.30957
1980	43.62843
1981	42.33764
1982	42.89051
1983	50.13973
1984	68.30215
1985	63.45149
1986	60.05595
1987	79.07849
1988	61.32082
1989	81.45397
1990	71.71827
1991	66.71052
1992	66.74836
1993	66.55035
1994	67.62786
1995	48.98965
1996	52.24579
1997	47.94115
1998	49.75304
1999	45.05033
2000	36.93501
2001	32.71958
2002	41.19593
2003	46.88008
2004	36.02837
2005	31.65016
2006	24.75835
2007	25.19229
2008	21.13807
2009	25.85517
2010	26.20537
2011	38.3061
2012	35.19045
2013	36.8381