Year	Percent
1960	2.95053
1961	3.3093
1962	3.58776
1963	3.73794
1964	3.72425
1965	3.60229
1966	3.46462
1967	3.35159
1968	3.30094
1969	3.30219
1970	3.34788
1971	3.397
1972	3.41059
1973	3.38886
1974	3.31968
1975	3.21531
1976	3.11217
1977	3.00887
1978	2.95733
1979	2.93758
1980	2.95135
1981	2.94549
1982	2.9296
1983	2.89453
1984	2.84714
1985	2.78259
1986	2.74224
1987	2.67121
1988	2.55587
1989	2.35121
1990	2.10029
1991	1.81877
1992	1.59598
1993	1.48887
1994	1.54031
1995	1.69508
1996	1.88139
1997	2.00813
1998	2.0549
1999	1.9839
2000	1.83157
2001	1.67809
2002	1.53536
2003	1.41561
2004	1.3097
2005	1.22806
2006	1.14918
2007	1.06554
2008	0.98708
2009	0.90855
2010	0.83952
2011	0.75252
2012	0.68692
2013	0.66944
2014	0.71256
2015	0.79758
2016	0.90268
2017	0.99394