Year	Percent
1960	5.52256
1961	6.61723
1962	6.83068
1963	6.7593
1964	6.73884
1965	6.72811
1966	5.89003
1967	3.26139
1968	3.30212
1969	3.28946
1970	3.24832
1971	3.19625
1972	3.1668
1973	3.15701
1974	3.17668
1975	3.21877
1976	3.25205
1977	3.92548
1978	5.00271
1979	5.0295
1980	5.06369
1981	5.0818
1982	5.08827
1983	5.05922
1984	4.99566
1985	4.89413
1986	4.79145
1987	4.61858
1988	4.35172
1989	4.219
1990	4.08156
1991	3.94504
1992	3.80859
1993	3.64888
1994	3.47438
1995	3.29222
1996	3.11729
1997	2.95068
1998	2.81832
1999	2.77817
2000	2.69548
2001	2.61623
2002	2.55844
2003	2.5337
2004	2.55071
2005	2.59548
2006	2.64799
2007	2.69612
2008	2.76095
2009	2.8176
2010	2.88414
2011	2.95002
2012	2.99677
2013	2.99068
2014	2.92344
2015	2.80889
2016	2.68418
2017	2.56488