Year	Percent
1960	4.77668
1961	4.78163
1962	4.74849
1963	4.70871
1964	4.66447
1965	4.61669
1966	4.56278
1967	4.50742
1968	4.48607
1969	4.49495
1970	4.48706
1971	4.47049
1972	4.47454
1973	4.42376
1974	4.31213
1975	4.15616
1976	3.99611
1977	3.84668
1978	3.71144
1979	3.58817
1980	3.45949
1981	3.12195
1982	3.02651
1983	2.9448
1984	2.87226
1985	2.81046
1986	2.74897
1987	2.69113
1988	2.65541
1989	2.64581
1990	2.61429
1991	2.54204
1992	2.5433
1993	2.51265
1994	2.44338
1995	2.3437
1996	2.14154
1997	2.00336
1998	1.91737
1999	1.82881
2000	1.7817
2001	1.74726
2002	1.66795
2003	1.64344
2004	1.68997
2005	1.77905
2006	1.88538
2007	1.96768
2008	2.01093
2009	1.99399
2010	1.93787
2011	1.87801
2012	1.82477
2013	1.77768
2014	1.73912
2015	1.70387
2016	1.66935
2017	1.62816