Year	Percent
1960	3.0522
1961	3.14659
1962	3.22001
1963	3.20658
1964	3.12316
1965	2.96641
1966	2.80904
1967	2.64663
1968	2.43885
1969	2.1668
1970	1.8739
1971	1.56821
1972	1.28571
1973	1.05872
1974	0.89065
1975	0.77319
1976	0.66036
1977	0.5608
1978	0.49471
1979	0.48775
1980	0.51367
1981	0.55836
1982	0.62136
1983	0.62131
1984	0.566
1985	0.46851
1986	0.34994
1987	0.26305
1988	0.25183
1989	0.35681
1990	0.53438
1991	0.7402
1992	0.90643
1993	0.98385
1994	0.94109
1995	0.80781
1996	0.65956
1997	0.53278
1998	0.45368
1999	0.44645
2000	0.49087
2001	0.54601
2002	0.57703
2003	0.60975
2004	0.62787
2005	0.64007
2006	0.64539
2007	0.65606
2008	0.67795
2009	0.70585
2010	0.74334
2011	0.78102
2012	0.81145
2013	0.82274
2014	0.80043
2015	0.76105
2016	0.70253
2017	0.67167