Year	Percent
1965	31.57625
1966	32.18303
1967	32.43071
1968	27.97104
1969	26.03776
1970	32.90615
1971	34.14677
1972	31.15283
1973	33.2007
1974	36.49845
1975	37.44625
1976	38.88761
1977	38.10642
1978	29.93833
1979	28.6018
1980	28.28807
1981	27.76887
1982	28.76127
1983	26.379
1984	27.52633
1985	27.4999
1986	32.89169
1987	31.49029
1988	30.37929
1989	27.39153
1990	24.58392
1991	22.17212
1992	21.51107
1993	22.02478
1994	22.92634
1995	23.96555
1996	22.66234
1997	24.92719
1998	28.16792
1999	24.45838
2000	21.74442
2001	20.48057
2002	20.46929
2003	19.58418
2004	21.65725
2005	22.59322
2006	24.17145
2007	27.32603
2008	26.11512
2009	24.71794
2010	25.41443
2011	25.9003
2012	26.48398
2013	27.86985
2014	28.06568
2015	27.57165
2016	29.31786
2017	28.76907