Year	Percent
1960	4.51814
1961	4.50437
1962	4.50178
1963	4.49046
1964	4.48266
1965	4.47024
1966	4.47606
1967	4.78018
1968	4.93654
1969	4.88967
1970	4.84676
1971	4.81082
1972	4.79634
1973	4.80676
1974	4.86682
1975	4.95029
1976	5.01985
1977	4.83896
1978	4.83021
1979	5.02176
1980	5.23391
1981	5.40888
1982	5.51681
1983	5.55788
1984	5.52376
1985	5.41743
1986	5.33625
1987	4.93725
1988	4.58479
1989	4.12261
1990	3.5671
1991	2.96891
1992	2.90718
1993	2.73694
1994	2.69702
1995	2.84528
1996	3.05233
1997	3.0604
1998	3.06124
1999	2.96177
2000	2.76692
2001	2.55982
2002	2.40361
2003	2.28219
2004	2.20998
2005	2.17438
2006	2.1411
2007	2.0331
2008	1.9832
2009	1.99084
2010	2.01313
2011	2.04107
2012	2.04273
2013	2.02576
2014	1.98945
2015	1.92588
2016	1.85785
2017	1.79015