Year	Percent
1960	4.30583
1961	3.87081
1962	4.05266
1963	4.00545
1964	3.76896
1965	3.63899
1966	3.49447
1967	3.27723
1968	3.30256
1969	3.0476
1970	2.49156
1971	2.78807
1972	3.24792
1973	4.24135
1974	4.9298
1975	4.70472
1976	4.51047
1977	4.29846
1978	4.55595
1979	5.16284
1980	5.91161
1981	7.44758
1982	11.01963
1983	9.5178
1984	9.52669
1985	8.3368
1986	8.71218
1987	12.48213
1988	14.38232
1989	11.84433
1990	13.61471
1991	14.48788
1992	15.65822
1993	16.70229
1994	18.53675
1995	17.95102
1996	17.9233
1997	19.49316
1998	18.34232
1999	18.1627
2000	20.89344
2001	20.31215
2002	22.64475
2003	26.98076
2004	31.06134
2005	33.82986
2006	36.03503
2007	35.38818
2008	32.51957
2009	24.45665
2010	26.26741
2011	26.49432
2012	25.4082
2013	24.50498
2014	23.49506
2015	21.34807
2016	19.65838
2017	19.75738