Year	Percent
1960	5.6825
1961	6.35612
1962	6.36498
1963	6.28185
1964	6.18995
1965	6.08088
1966	5.97859
1967	5.86884
1968	5.76581
1969	5.64732
1970	5.54728
1971	5.44189
1972	5.33603
1973	5.22042
1974	5.11831
1975	5.00753
1976	4.9041
1977	4.7953
1978	4.69828
1979	4.60578
1980	4.51992
1981	4.42886
1982	3.48063
1983	2.7265
1984	2.68665
1985	2.64459
1986	2.60336
1987	2.56349
1988	2.52816
1989	2.4967
1990	2.47011
1991	2.44658
1992	2.41764
1993	2.37846
1994	3.11095
1995	3.26136
1996	3.17007
1997	3.07824
1998	3.00708
1999	2.95214
2000	2.90827
2001	2.86496
2002	2.82214
2003	3.45076
2004	3.63764
2005	3.51742
2006	3.40724
2007	3.29802
2008	3.19256
2009	3.07963
2010	2.98002
2011	2.74168
2012	2.56163
2013	2.47808
2014	2.397
2015	2.31782
2016	2.23832
2017	2.15708