Year	Percent
1960	1.26528
1961	1.50732
1962	1.73833
1963	1.83886
1964	2.04937
1965	2.14445
1966	2.16607
1967	2.3156
1968	2.21015
1969	2.06886
1970	1.87403
1971	1.68921
1972	1.5427
1973	1.3635
1974	1.11419
1975	0.93024
1976	0.63752
1977	0.45425
1978	0.66814
1979	1.21191
1980	1.9272
1981	2.80522
1982	3.44847
1983	3.98379
1984	4.35881
1985	4.40248
1986	4.65542
1987	4.56489
1988	4.53603
1989	4.0691
1990	3.46748
1991	2.83295
1992	2.39232
1993	2.04875
1994	1.95224
1995	2.05605
1996	2.17937
1997	2.29388
1998	2.31853
1999	2.33536
2000	2.23848
2001	2.10887
2002	2.0839
2003	2.16416
2004	2.42934
2005	2.74361
2006	3.13156
2007	3.39699
2008	3.46911
2009	3.23941
2010	2.89562
2011	2.45636
2012	2.15573
2013	1.90052
2014	1.81439
2015	1.75881
2016	1.80345
2017	1.72984