Year	Percent
1960	64.45384
1961	58.72082
1962	56.14154
1963	45.92754
1964	44.28208
1965	45.10283
1966	43.39709
1967	41.16583
1968	43.432
1969	47.42102
1970	45.82812
1971	40.65244
1972	36.18244
1973	41.67859
1974	48.53797
1975	45.75972
1976	52.06293
1977	50.37449
1978	49.20945
1979	56.19042
1980	57.72594
1981	52.50361
1982	51.03313
1983	50.97334
1984	54.43981
1985	55.08051
1986	56.4738
1987	62.8945
1988	66.4155
1989	71.37685
1990	74.46612
1991	77.82613
1992	75.98436
1993	78.92075
1994	89.15123
1995	94.08959
1996	91.57691
1997	93.28945
1998	115.74332
1999	121.31059
2000	119.80999
2001	110.40249
2002	108.30559
2003	106.94321
2004	115.37309
2005	112.89898
2006	112.18567
2007	106.16858
2008	99.49977
2009	91.4168
2010	86.9303
2011	85.25544
2012	79.29991
2013	75.62904
2014	73.7935
2015	70.60152
2016	67.66722
2017	71.47345