Year	Percent
1960	5.79515
1961	5.82969
1962	5.87467
1963	6.52677
1964	6.64648
1965	6.64882
1966	6.68212
1967	6.71445
1968	6.74129
1969	6.77589
1970	7.89799
1971	8.12102
1972	8.15653
1973	8.16137
1974	8.17023
1975	8.16712
1976	8.17232
1977	8.13898
1978	8.13481
1979	8.12526
1980	4.97172
1981	4.44211
1982	4.44718
1983	4.42474
1984	4.38502
1985	4.32216
1986	4.2609
1987	4.19243
1988	4.1239
1989	4.04351
1990	4.92611
1991	5.01268
1992	4.93155
1993	4.84825
1994	4.76275
1995	4.67898
1996	4.60346
1997	4.52696
1998	4.47818
1999	4.44382
2000	4.47436
2001	4.46116
2002	4.44823
2003	4.4419
2004	4.44182
2005	4.43557
2006	4.43906
2007	4.43884
2008	4.43227
2009	4.40908
2010	4.38819
2011	4.38624
2012	4.37694
2013	4.36839
2014	4.34364
2015	4.31718
2016	4.28807
2017	4.25858