Year	Percent
1960	22.90452
1961	28.10354
1962	25.74693
1963	23.51987
1964	24.72277
1965	30.12422
1966	28.69636
1967	28.79129
1968	27.99496
1969	27.06979
1970	29.10763
1971	28.42733
1972	29.00665
1973	33.23198
1974	38.37618
1975	36.58478
1976	36.24775
1977	36.33056
1978	37.43549
1979	37.66261
1980	41.17866
1981	42.2842
1982	39.32679
1983	35.72032
1984	31.79127
1985	32.3976
1986	30.18145
1987	29.62026
1988	27.89014
1989	29.05521
1990	27.11162
1991	26.98609
1992	28.11558
1993	25.90607
1994	29.30926
1995	34.44304
1996	32.41828
1997	35.29209
1998	34.97024
1999	34.13762
2000	33.85678
2001	32.85029
2002	32.40131
2003	33.37607
2004	38.20167
2005	44.02428
2006	42.70214
2007	42.21165
2008	40.15877
2009	39.92479
2010	43.32679
2011	37.33487
2012	44.33196
2013	38.59578
2014	25.70872
2015	25.84275
2016	20.16081
2017	19.40277