Year	Percent
1965	21.92321
1966	25.05336
1967	27.27097
1968	25.76221
1969	26.58269
1970	26.14111
1971	26.98032
1972	27.63045
1973	28.05476
1974	28.46254
1975	31.63115
1976	31.34079
1977	29.50448
1978	28.97118
1979	30.02291
1980	28.29136
1981	27.63176
1982	28.60372
1983	29.03039
1984	28.34353
1985	18.05525
1986	23.66611
1987	20.69756
1988	25.4373
1989	31.89436
1990	31.4114
1991	32.36509
1992	30.71262
1993	30.51725
1994	31.01299
1995	30.37259
1996	31.62766
1997	29.98722
1998	30.38222
1999	30.81096
2000	29.58747
2001	27.40518
2002	28.87062
2003	29.2333
2004	29.46486
2005	28.14474
2006	28.96878
2007	28.55519
2008	27.66694
2009	25.91782
2010	25.79121
2011	26.12929
2012	25.76285
2013	26.61406
2014	27.094
2015	25.66429
2016	24.42842
2017	24.83047