Year	Percent
1960	2.70747
1961	2.72374
1962	2.7409
1963	2.76295
1964	2.79163
1965	2.8244
1966	2.84638
1967	2.86231
1968	2.88925
1969	2.92924
1970	2.97175
1971	3.02946
1972	3.06649
1973	3.03259
1974	2.91363
1975	2.74927
1976	2.56921
1977	2.43551
1978	2.3938
1979	2.46859
1980	2.61838
1981	2.78061
1982	2.90878
1983	3.00235
1984	3.04842
1985	3.05973
1986	3.05882
1987	3.05968
1988	3.05812
1989	3.0567
1990	3.05068
1991	3.05051
1992	3.0354
1993	2.97466
1994	2.86004
1995	2.71685
1996	2.56743
1997	2.44859
1998	2.38385
1999	2.38744
2000	2.43837
2001	2.50226
2002	2.55588
2003	2.60249
2004	2.63533
2005	2.65985
2006	2.67902
2007	2.7043
2008	2.74464
2009	2.80335
2010	2.86909
2011	2.93479
2012	2.98198
2013	2.99627
2014	2.97088
2015	2.91916
2016	2.86061
2017	2.80839