Year	Percent
1960	2.58865
1961	2.70324
1962	2.76383
1963	2.74895
1964	2.65944
1965	2.51467
1966	2.33137
1967	2.2076
1968	2.22633
1969	2.4187
1970	2.72936
1971	3.07067
1972	3.34684
1973	3.46328
1974	3.3882
1975	3.21857
1976	2.99174
1977	2.85302
1978	2.83098
1979	2.97364
1980	3.20712
1981	3.44412
1982	3.60931
1983	3.69416
1984	3.67246
1985	3.58824
1986	3.48227
1987	3.38822
1988	3.27431
1989	3.14695
1990	3.01062
1991	2.88737
1992	2.76274
1993	2.61961
1994	2.43406
1995	2.24839
1996	2.04328
1997	1.89004
1998	1.84867
1999	1.94161
2000	2.12671
2001	2.34162
2002	2.51627
2003	2.63799
2004	2.68171
2005	2.6741
2006	2.64172
2007	2.62254
2008	2.63815
2009	2.70102
2010	2.78456
2011	2.87186
2012	2.90878
2013	2.85726
2014	2.69366
2015	2.45727
2016	2.21079
2017	1.98459