Year	Percent
1960	3.75059
1961	3.73678
1962	3.71919
1963	3.72008
1964	3.74116
1965	3.75632
1966	3.7864
1967	3.80429
1968	3.86536
1969	3.93603
1970	4.02113
1971	4.12118
1972	4.20799
1973	4.25611
1974	4.27557
1975	4.2601
1976	4.22558
1977	4.2989
1978	4.3958
1979	4.44501
1980	4.51604
1981	4.60839
1982	4.67872
1983	4.65698
1984	4.5187
1985	4.31086
1986	4.07593
1987	3.79454
1988	3.24462
1989	3.40007
1990	3.68626
1991	4.01155
1992	4.27781
1993	4.43441
1994	4.47734
1995	4.42797
1996	4.3647
1997	4.32841
1998	4.52891
1999	5.24585
2000	5.34636
2001	5.42924
2002	5.49804
2003	5.55352
2004	5.60615
2005	5.62958
2006	5.67112
2007	5.68281
2008	5.65283
2009	5.54942
2010	5.40152
2011	5.24172
2012	5.10313
2013	5.00376
2014	4.95795
2015	4.94195
2016	4.93305
2017	4.91141