Year	Percent
1960	2.2265
1961	2.22388
1962	2.21826
1963	2.21013
1964	2.19964
1965	2.18498
1966	2.17029
1967	2.14784
1968	2.10604
1969	2.04047
1970	1.95995
1971	1.87818
1972	1.8037
1973	1.73578
1974	1.67718
1975	1.62764
1976	1.58105
1977	1.54047
1978	1.5151
1979	1.508
1980	1.51465
1981	1.52318
1982	1.53282
1983	1.55212
1984	1.58202
1985	1.61689
1986	1.65344
1987	1.6818
1988	1.6918
1989	1.67818
1990	1.64718
1991	1.6114
1992	1.57617
1993	1.53619
1994	1.49227
1995	1.44588
1996	1.39761
1997	1.34974
1998	1.30431
1999	1.26281
2000	1.22483
2001	1.18678
2002	1.15015
2003	1.11961
2004	1.09676
2005	1.07897
2006	1.06404
2007	1.04778
2008	1.02708
2009	1.00027
2010	0.96925
2011	0.93716
2012	0.90758
2013	0.88136
2014	0.85992
2015	0.84171
2016	0.82458
2017	0.8062