Year	Percent
1960	2.54642
1961	2.75326
1962	2.92431
1963	3.02491
1964	3.0359
1965	2.98972
1966	2.92284
1967	2.87333
1968	2.84967
1969	2.86712
1970	2.90464
1971	2.94527
1972	2.96388
1973	2.95115
1974	2.90041
1975	2.82575
1976	2.7473
1977	2.68216
1978	2.63411
1979	2.6083
1980	2.598
1981	2.56232
1982	2.52075
1983	2.52664
1984	2.59192
1985	2.67832
1986	2.79266
1987	2.84503
1988	2.7346
1989	2.42495
1990	1.99477
1991	1.53445
1992	1.14691
1993	0.87417
1994	0.76132
1995	0.76632
1996	0.80302
1997	0.82231
1998	0.84817
1999	0.86954
2000	0.89133
2001	0.92751
2002	0.98215
2003	1.04325
2004	1.10937
2005	1.17908
2006	1.24168
2007	1.30721
2008	1.39705
2009	1.51645
2010	1.64886
2011	1.78538
2012	1.89075
2013	1.93136
2014	1.89161
2015	1.79578
2016	1.68287
2017	1.58118