Year	Percent
1960	42.18458
1961	47.18953
1962	35.42061
1963	28.94066
1964	21.84661
1965	22.60394
1966	17.32413
1967	23.43442
1968	27.86792
1969	32.35274
1970	36.64907
1971	35.28134
1972	34.30249
1973	40.2842
1974	40.01654
1975	45.40683
1976	43.35028
1977	46.91474
1978	52.21935
1979	42.54593
1980	39.07692
1981	36.99059
1982	37.28324
1983	37.56953
1984	35.16442
1985	34.56917
1986	33.55592
1987	27.55638
1988	27.63948
1989	30.07323
1990	28.58942
1991	31.84133
1992	30.75749
1993	29.09091
1994	30.08014
1995	30.90856
1996	25.67841
1997	22.44697
1998	27.14848
1999	26.24767
2000	23.56391
2001	26.84106
2002	30.65337
2003	30.34066
2004	33.26354
2005	31.65641
2006	30.17046
2007	34.46948
2008	37.34844
2009	46.87646
2010	41.43029
2011	38.05506
2012	39.15828
2013	43.3906
2014	45.55443
2015	50.68896
2016	50.70906
2017	47.78354