Year	Percent
1960	5.40099
1961	5.71011
1962	5.67797
1963	5.63403
1964	5.49821
1965	5.28969
1966	5.02389
1967	4.71272
1968	4.56827
1969	4.30388
1970	4.43672
1971	4.18878
1972	4.1345
1973	4.13467
1974	4.12817
1975	3.81293
1976	3.91624
1977	3.81544
1978	3.85546
1979	3.79904
1980	3.99373
1981	4.08053
1982	4.38083
1983	4.30698
1984	4.09393
1985	4.16942
1986	4.68114
1987	4.31767
1988	4.16853
1989	4.05853
1990	3.92753
1991	3.75279
1992	2.41727
1993	1.45318
1994	1.30754
1995	1.36462
1996	1.22461
1997	1.13761
1998	1.21996
1999	1.32265
2000	1.69831
2001	1.85127
2002	2.17278
2003	3.09798
2004	3.40018
2005	3.40884
2006	3.141
2007	3.02647
2008	2.90091
2009	2.87257
2010	2.74038
2011	2.73475
2012	2.69477
2013	2.62406
2014	2.47901
2015	2.44948
2016	2.39091
2017	2.29152