Year	Percent
1960	4.26892
1961	4.67428
1962	4.79911
1963	4.80336
1964	4.8301
1965	4.84027
1966	4.84975
1967	4.87422
1968	4.89089
1969	4.91419
1970	4.95399
1971	5.67348
1972	6.25917
1973	6.29086
1974	6.39881
1975	6.50192
1976	6.61239
1977	6.65695
1978	6.63219
1979	6.489
1980	6.29424
1981	8.94118
1982	9.0194
1983	8.66468
1984	8.14486
1985	7.51518
1986	6.80358
1987	6.21209
1988	6.08471
1989	6.53643
1990	7.42578
1991	4.49517
1992	5.38118
1993	5.84448
1994	5.7756
1995	5.37639
1996	4.92286
1997	4.59684
1998	3.29653
1999	3.19858
2000	3.32224
2001	3.45647
2002	3.53348
2003	3.57903
2004	3.58744
2005	3.56577
2006	3.54873
2007	3.5323
2008	4.45355
2009	4.51738
2010	4.51099
2011	4.49683
2012	4.4796
2013	4.46124
2014	4.44153
2015	4.42049
2016	4.3987
2017	4.37315