Year	Percent
1960	31.09575
1961	32.71717
1962	32.03781
1963	32.03295
1964	33.38941
1965	31.39732
1966	32.41163
1967	28.46433
1968	29.40081
1969	29.52866
1970	29.82573
1971	28.63936
1972	26.58783
1973	27.39383
1974	33.67588
1975	29.82369
1976	32.45047
1977	34.95887
1978	28.93552
1979	25.75315
1980	29.51696
1981	30.45988
1982	26.65747
1983	25.94993
1984	26.74989
1985	25.29893
1986	25.84836
1987	21.30522
1988	22.37121
1989	23.03303
1990	25.69261
1991	27.04163
1992	26.26037
1993	38.90363
1994	37.04028
1995	32.5917
1996	25.2006
1997	22.68639
1998	20.16926
1999	20.83274
2000	21.58757
2001	22.93158
2002	24.89797
2003	24.08682
2004	26.61026
2005	28.50903
2006	22.98494
2007	21.91899
2008	22.67406
2009	20.03263
2010	20.65698
2011	21.62519
2012	22.26182
2013	19.92539
2014	18.29698
2015	16.59244
2016	13.97122
2017	13.93121