Year	Percent
1960	2.9603
1961	2.93452
1962	2.91158
1963	2.89787
1964	2.89596
1965	2.89963
1966	2.90294
1967	2.89895
1968	2.88413
1969	2.85619
1970	2.81927
1971	2.78362
1972	2.74862
1973	2.70582
1974	2.6539
1975	2.5984
1976	2.53964
1977	2.4888
1978	2.45848
1979	2.45366
1980	2.4646
1981	2.48189
1982	2.49106
1983	2.48561
1984	2.45979
1985	2.42183
1986	2.38093
1987	2.34824
1988	2.32788
1989	2.3238
1990	2.32996
1991	2.34135
1992	2.34771
1993	2.34291
1994	2.32326
1995	2.29537
1996	2.26258
1997	2.23801
1998	2.2331
1999	2.25315
2000	2.28798
2001	2.32626
2002	2.35284
2003	2.36059
2004	2.3438
2005	2.31041
2006	2.27224
2007	2.23853
2008	2.20952
2009	2.18804
2010	2.17104
2011	2.15363
2012	2.13203
2013	2.10689
2014	2.07715
2015	2.04427
2016	2.01037
2017	1.97662