Year	Percent
1960	2.78822
1961	2.83743
1962	2.87989
1963	2.90352
1964	2.9022
1965	2.88474
1966	2.86669
1967	2.85469
1968	2.83911
1969	2.82146
1970	2.80409
1971	2.7843
1972	2.76969
1973	2.77012
1974	2.78917
1975	2.81972
1976	2.85401
1977	2.88225
1978	2.89763
1979	2.89713
1980	2.88649
1981	2.88185
1982	2.88428
1983	2.8821
1984	2.87486
1985	2.86877
1986	2.86233
1987	2.87021
1988	2.91033
1989	2.98851
1990	3.09071
1991	3.19464
1992	3.28696
1993	3.36961
1994	3.43865
1995	3.49564
1996	3.55145
1997	3.60135
1998	3.63154
1999	3.63947
2000	3.63385
2001	3.62421
2002	3.6206
2003	3.62724
2004	3.64719
2005	3.67533
2006	3.70208
2007	3.7245
2008	3.7479
2009	3.77198
2010	3.79496
2011	3.81685
2012	3.8342
2013	3.84326
2014	3.84268
2015	3.83575
2016	3.82607
2017	3.81709