Year	Percent
1960	2.33269
1961	2.5864
1962	3.0466
1963	3.06818
1964	3.09062
1965	3.09096
1966	3.0967
1967	3.10623
1968	3.12441
1969	3.16071
1970	3.21219
1971	3.42101
1972	3.93944
1973	3.94866
1974	3.9551
1975	3.93198
1976	3.90663
1977	3.88505
1978	3.87232
1979	3.87231
1980	3.88326
1981	3.68884
1982	3.29908
1983	3.28964
1984	3.26434
1985	3.22383
1986	3.18464
1987	3.14315
1988	3.10566
1989	3.06928
1990	3.02611
1991	2.93884
1992	2.79886
1993	2.76469
1994	2.73577
1995	2.70622
1996	2.68482
1997	2.6572
1998	2.6259
1999	2.58973
2000	2.55004
2001	2.63786
2002	2.85713
2003	2.81272
2004	2.77286
2005	2.72637
2006	2.68488
2007	2.64534
2008	2.60017
2009	2.54132
2010	2.48195
2011	2.42432
2012	2.39935
2013	2.37913
2014	2.37281
2015	2.37378
2016	2.37627
2017	2.37892