Year	Percent
1960	5.94148
1961	5.89547
1962	5.86996
1963	5.87613
1964	5.9142
1965	5.96251
1966	6.03293
1967	6.0602
1968	5.97805
1969	5.74431
1970	5.42507
1971	5.11089
1972	4.83964
1973	4.60311
1974	4.45707
1975	4.36518
1976	4.29017
1977	4.23243
1978	4.32863
1979	4.58557
1980	4.96274
1981	5.3943
1982	5.82328
1983	5.0801
1984	3.76557
1985	3.86315
1986	3.84748
1987	3.8947
1988	4.19996
1989	4.83257
1990	5.6021
1991	6.38468
1992	6.8728
1993	6.81649
1994	6.18858
1995	5.24062
1996	4.26266
1997	3.4375
1998	2.86095
1999	2.64711
2000	2.66431
2001	2.71596
2002	2.71801
2003	2.75119
2004	2.79533
2005	2.84907
2006	2.93259
2007	3.0214
2008	3.07922
2009	3.09279
2010	3.08206
2011	3.05964
2012	3.05464
2013	3.07948
2014	3.14288
2015	3.26565
2016	3.3899
2017	3.49328