Year	Percent
1960	12.71217
1961	12.58905
1962	12.4529
1963	12.36471
1964	12.36011
1965	12.34525
1966	12.15384
1967	10.18962
1968	10.24531
1969	10.25544
1970	10.29285
1971	10.3206
1972	10.35198
1973	10.31378
1974	10.28953
1975	10.23205
1976	10.20001
1977	5.98591
1978	5.22497
1979	5.17743
1980	5.12488
1981	5.00136
1982	4.92078
1983	4.99887
1984	5.29143
1985	5.6673
1986	6.08406
1987	6.34991
1988	6.32722
1989	5.9512
1990	5.38265
1991	4.76087
1992	4.25345
1993	3.92651
1994	3.85688
1995	3.94273
1996	4.09666
1997	3.8069
1998	1.59553
1999	1.31721
2000	0.92786
2001	0.49461
2002	0.16515
2003	0.01898
2004	0.11707
2005	0.40416
2006	0.73301
2007	1.21617
2008	2.76612
2009	2.84129
2010	2.83456
2011	2.82044
2012	2.50596
2013	2.50353
2014	2.49243
2015	2.47998
2016	2.4895
2017	2.48786