Year	Percent
1960	2.19676
1961	2.22532
1962	2.25586
1963	2.2904
1964	2.33049
1965	2.37495
1966	2.42079
1967	2.46757
1968	2.5172
1969	2.57017
1970	2.62519
1971	2.67856
1972	2.73072
1973	2.78675
1974	2.84612
1975	2.9062
1976	3.01296
1977	3.11926
1978	3.13662
1979	3.04415
1980	2.90978
1981	2.63395
1982	2.44912
1983	2.69161
1984	3.46077
1985	4.46911
1986	5.58501
1987	6.28693
1988	6.17062
1989	5.16409
1990	3.70081
1991	2.1344
1992	0.91441
1993	0.2683
1994	0.42059
1995	1.13785
1996	2.00518
1997	2.65561
1998	3.06268
1999	3.12325
2000	2.96015
2001	2.77142
2002	2.68134
2003	2.65289
2004	2.71359
2005	2.8286
2006	2.94367
2007	3.01969
2008	3.06129
2009	3.05944
2010	3.02879
2011	2.99115
2012	2.96121
2013	2.93732
2014	2.92294
2015	2.91437
2016	2.90482
2017	2.89029