Year	Percent
1960	2.2987
1961	2.30466
1962	2.31273
1963	2.32416
1964	2.33847
1965	2.35511
1966	2.34787
1967	2.33895
1968	2.37188
1969	2.45631
1970	2.56167
1971	2.70944
1972	2.80491
1973	2.72393
1974	2.42567
1975	2.00624
1976	1.54123
1977	1.1827
1978	1.04688
1979	1.20717
1980	1.57195
1981	1.98237
1982	2.31592
1983	2.57545
1984	2.72485
1985	2.7913
1986	2.83756
1987	2.88673
1988	2.90558
1989	2.89559
1990	2.85992
1991	2.8155
1992	2.7537
1993	2.6502
1994	2.50129
1995	2.32578
1996	2.14619
1997	1.98413
1998	1.84666
1999	1.74216
2000	1.66541
2001	1.58725
2002	1.51591
2003	1.4875
2004	1.511
2005	1.56626
2006	1.64318
2007	1.70239
2008	1.70648
2009	1.63629
2010	1.5202
2011	1.38658
2012	1.28144
2013	1.22991
2014	1.25226
2015	1.32279
2016	1.40643
2017	1.466