Year	Percent
1960	5.04483
1961	4.99216
1962	4.9555
1963	4.91899
1964	4.68129
1965	3.80701
1966	3.80793
1967	3.79877
1968	3.77874
1969	3.74854
1970	3.70375
1971	3.66871
1972	3.62595
1973	3.57823
1974	3.51334
1975	3.45326
1976	3.39255
1977	3.33713
1978	3.29971
1979	3.29307
1980	3.29961
1981	3.31254
1982	3.31485
1983	3.30773
1984	3.2777
1985	3.23309
1986	3.18814
1987	3.15141
1988	3.12949
1989	3.11664
1990	3.12132
1991	3.1265
1992	3.12909
1993	3.11826
1994	3.09492
1995	3.06342
1996	3.02704
1997	2.99443
1998	2.98831
1999	3.00271
2000	3.03416
2001	3.06471
2002	3.08808
2003	3.03864
2004	2.98513
2005	2.94551
2006	2.90332
2007	2.86778
2008	2.83691
2009	2.80737
2010	2.79068
2011	2.7674
2012	2.7441
2013	2.73958
2014	2.73004
2015	2.72094
2016	2.70437
2017	2.69148