Year	Percent
1960	2.78263
1961	3.38571
1962	3.97385
1963	4.42961
1964	4.7579
1965	4.92744
1966	5.13304
1967	5.26449
1968	5.04008
1969	4.40882
1970	3.54374
1971	2.75647
1972	2.09479
1973	1.60579
1974	1.57168
1975	1.87523
1976	2.26884
1977	2.57345
1978	2.86969
1979	3.09928
1980	3.63105
1981	7.80142
1982	7.90945
1983	7.87342
1984	7.69745
1985	7.39119
1986	8.90832
1987	8.49639
1988	8.2315
1989	8.13272
1990	8.09121
1991	4.39994
1992	4.6242
1993	4.72706
1994	4.67865
1995	4.5296
1996	4.34994
1997	4.19035
1998	4.04596
1999	3.91766
2000	3.79748
2001	3.55522
2002	3.43556
2003	3.29466
2004	3.12489
2005	2.93746
2006	2.74956
2007	2.58148
2008	2.47092
2009	2.41628
2010	2.39566
2011	1.93209
2012	1.95433
2013	1.97154
2014	1.98523
2015	1.98774
2016	1.98963
2017	1.99093