Year	Percent
1960	3.36698
1961	3.34847
1962	3.31669
1963	3.31044
1964	2.93198
1965	2.93839
1966	2.96503
1967	2.96673
1968	2.93782
1969	2.85837
1970	2.75108
1971	2.63837
1972	2.53408
1973	2.4634
1974	2.42541
1975	2.4174
1976	2.41239
1977	2.39512
1978	2.36179
1979	2.29911
1980	2.21316
1981	1.93759
1982	1.40327
1983	1.35064
1984	1.33766
1985	1.33561
1986	1.3433
1987	1.34237
1988	1.31109
1989	1.26373
1990	1.18549
1991	1.1231
1992	1.05304
1993	0.9727
1994	0.85592
1995	0.73744
1996	0.59595
1997	0.48522
1998	0.42165
1999	0.44696
2000	0.51556
2001	0.61402
2002	0.68313
2003	0.73341
2004	0.73309
2005	0.69429
2006	0.66093
2007	0.62491
2008	0.59725
2009	0.56372
2010	0.52441
2011	0.4936
2012	0.45752
2013	0.79128
2014	1.00937
2015	1.14279
2016	1.42487
2017	1.5281