Year	Percent
1967	31.18557
1968	12.57942
1969	9.3
1970	13.76404
1971	28.45723
1972	29.82955
1973	26.21015
1974	30.62445
1975	35.62552
1976	35.85887
1977	30.6189
1978	28.89592
1979	26.01007
1980	22.29321
1981	22.95697
1982	26.59616
1983	26.48272
1984	29.97144
1985	27.57892
1986	32.11209
1987	18.78871
1988	15.85053
1989	12.32656
1990	12.34837
1991	15.02018
1992	16.35373
1993	17.53477
1994	15.74296
1995	14.97993
1996	13.69525
1997	17.64513
1998	23.9802
1999	14.8505
2000	15.37077
2001	17.2115
2002	19.00476
2003	23.20093
2004	27.90182
2005	21.42582
2006	27.15189
2007	34.2774
2008	36.48887
2009	28.20755
2010	25.41759
2011	23.79951
2012	27.75173
2013	29.81652
2014	24.74386
2015	36.36068