Year	Percent
1960	4.42827
1961	3.48941
1962	2.90828
1963	2.85989
1964	2.86414
1965	3.18916
1966	3.23503
1967	2.97626
1968	2.91841
1969	2.40546
1970	2.46085
1971	2.13277
1972	2.50744
1973	3.7588
1974	5.40368
1975	4.84948
1976	4.32644
1977	4.08615
1978	5.09419
1979	5.92373
1980	6.51324
1981	7.4496
1982	8.67334
1983	8.4033
1984	9.50592
1985	12.37605
1986	11.1693
1987	12.37553
1988	15.68245
1989	13.26137
1990	10.65842
1991	11.46185
1992	14.4875
1993	19.35378
1994	17.23307
1995	16.32308
1996	15.89145
1997	15.03985
1998	14.08237
1999	15.36187
2000	18.51709
2001	18.21521
2002	20.10266
2003	24.82323
2004	28.44419
2005	28.37804
2006	28.44386
2007	26.71644
2008	24.9333
2009	20.14878
2010	22.62189
2011	24.10551
2012	22.69966
2013	22.06025
2014	21.3815
2015	18.10499
2016	17.37544
2017	18.04602