Year	Percent
1960	5.21746
1961	4.28609
1962	3.69718
1963	3.84392
1964	4.85105
1965	6.25452
1966	7.65282
1967	8.45358
1968	8.40923
1969	7.51693
1970	6.21857
1971	4.97573
1972	4.04679
1973	3.36665
1974	2.9977
1975	2.85607
1976	2.73271
1977	2.61017
1978	2.65092
1979	2.86996
1980	3.19949
1981	3.58922
1982	3.92509
1983	4.12334
1984	4.14744
1985	4.07204
1986	3.90466
1987	3.79954
1988	3.91095
1989	4.28337
1990	4.76135
1991	5.27469
1992	5.56412
1993	5.42528
1994	4.81194
1995	3.94641
1996	3.08916
1997	2.42756
1998	1.95997
1999	1.74979
2000	1.74408
2001	1.75503
2002	1.79389
2003	2.04581
2004	2.53977
2005	3.17397
2006	3.77989
2007	4.27128
2008	4.67846
2009	4.9788
2010	5.16091
2011	5.32136
2012	5.36669
2013	5.13205
2014	4.59754
2015	3.89613
2016	3.18585
2017	2.57399