Year	Percent
1960	3.11841
1961	3.52745
1962	3.04371
1963	2.8654
1964	2.63519
1965	2.88571
1966	2.73592
1967	2.71363
1968	2.52707
1969	2.2609
1970	4.45045
1971	6.26482
1972	6.62541
1973	6.28382
1974	7.10956
1975	6.74254
1976	6.08505
1977	6.91524
1978	6.72812
1979	6.33256
1980	6.48209
1981	7.02212
1982	8.87727
1983	7.57522
1984	7.60541
1985	6.90061
1986	6.288
1987	5.63807
1988	4.14
1989	3.59003
1990	3.40165
1991	2.84984
1992	2.62851
1993	2.70692
1994	2.59754
1995	2.56206
1996	2.44932
1997	2.4982
1998	2.58984
1999	2.71363
2000	2.70205
2001	2.66708
2002	2.5518
2003	2.73385
2004	2.7087
2005	2.52137
2006	2.49073
2007	2.31702
2008	2.58401
2009	2.26361
2010	2.23947
2011	2.2544
2012	2.04629
2013	1.98642
2014	1.95516
2015	1.90946
2016	1.94185
2017	1.91006