Year	Percent
1960	3.06307
1961	3.15375
1962	3.20699
1963	3.1844
1964	3.0711
1965	2.90321
1966	2.72756
1967	2.5832
1968	2.47387
1969	2.41221
1970	2.38619
1971	2.3632
1972	2.34002
1973	2.34289
1974	2.37427
1975	2.42286
1976	2.48903
1977	2.54693
1978	2.56654
1979	2.53656
1980	2.47955
1981	2.40392
1982	2.35494
1983	2.3763
1984	2.486
1985	2.64588
1986	2.81971
1987	2.94807
1988	2.99539
1989	2.94194
1990	2.82442
1991	2.68631
1992	2.57469
1993	2.50479
1994	2.49204
1995	2.51333
1996	2.54223
1997	2.54544
1998	2.51
1999	2.42507
2000	2.30944
2001	2.18972
2002	2.08746
2003	2.00423
2004	1.94703
2005	1.90937
2006	1.86934
2007	1.82792
2008	1.80597
2009	1.80687
2010	1.8196
2011	1.84274
2012	1.85222
2013	1.8217
2014	1.73958
2015	1.62474
2016	1.49932
2017	1.39148