Year	Percent
1965	18.3548
1966	18.36271
1967	24.40211
1968	25.22184
1969	24.82302
1970	29.78627
1971	30.13945
1972	31.01321
1973	30.2459
1974	31.6597
1975	31.81732
1976	31.88944
1977	32.33282
1978	35.4596
1979	32.22419
1980	32.60487
1981	38.47032
1982	38.48195
1983	37.71347
1984	35.92429
1985	35.47835
1986	39.38974
1987	44.45946
1988	43.64239
1989	42.27094
1990	42.82983
1991	46.92724
1992	48.05895
1993	47.93028
1994	29.07117
1995	40.02836
1996	34.72489
1997	35.42898
1998	35.77982
1999	45.10413
2000	46.87124
2001	44.47101
2002	46.22396
2003	44.33488
2004	43.57386
2005	44.06274
2006	44.54792
2007	48.08601
2008	49.24613
2009	48.74515
2010	49.38152
2011	46.98163
2012	47.53036
2013	47.73445
2014	47.16289
2015	47.868
2016	47.29258
2017	46.38416