Year	Percent
1960	3.56128
1961	3.33108
1962	3.10103
1963	2.86475
1964	2.65099
1965	2.58899
1966	2.60937
1967	2.52028
1968	2.62184
1969	2.95134
1970	3.43314
1971	3.85381
1972	4.22532
1973	4.71027
1974	5.32103
1975	5.92172
1976	6.52805
1977	6.88826
1978	6.74347
1979	6.06255
1980	5.1197
1981	4.12893
1982	3.36067
1983	2.92885
1984	2.92065
1985	3.18798
1986	3.52696
1987	3.73982
1988	3.77563
1989	3.58036
1990	3.25524
1991	2.96534
1992	2.65786
1993	2.47497
1994	2.46049
1995	2.53054
1996	2.61757
1997	2.76803
1998	3.10324
1999	3.65111
2000	4.31066
2001	4.83317
2002	5.25439
2003	5.76816
2004	6.37833
2005	6.93041
2006	7.53326
2007	7.81445
2008	7.37
2009	6.18336
2010	4.666
2011	3.03884
2012	1.77795
2013	1.24394
2014	1.67281
2015	2.71311
2016	3.91502
2017	4.72939