Year	Percent
1960	1.9
1961	1.93878
1962	1.96917
1963	1.97746
1964	1.95818
1965	1.92401
1966	1.87373
1967	1.84054
1968	1.86159
1969	1.95328
1970	2.08476
1971	2.24015
1972	2.3608
1973	2.39639
1974	2.32408
1975	2.18708
1976	2.04075
1977	1.94065
1978	1.90133
1979	1.94313
1980	2.04481
1981	2.15143
1982	2.25266
1983	2.38682
1984	2.55457
1985	2.73747
1986	2.93156
1987	3.10004
1988	3.20706
1989	3.23742
1990	3.2203
1991	3.19219
1992	3.18461
1993	3.20088
1994	3.2496
1995	3.31972
1996	3.37645
1997	3.42249
1998	3.4884
1999	3.57719
2000	3.67113
2001	3.76925
2002	3.83498
2003	3.83064
2004	3.74421
2005	3.61029
2006	3.46166
2007	3.34141
2008	3.26967
2009	3.25983
2010	3.28731
2011	3.32138
2012	3.33301
2013	3.31668
2014	3.26471
2015	3.19094
2016	3.11409
2017	3.04904