Year	Percent
1960	3.39984
1961	3.18662
1962	3.0032
1963	2.85475
1964	2.76282
1965	2.73384
1966	2.70117
1967	2.66914
1968	2.64536
1969	2.65122
1970	2.66926
1971	2.70162
1972	2.71933
1973	2.72375
1974	2.6968
1975	2.66691
1976	2.6283
1977	2.57891
1978	2.53447
1979	2.48603
1980	2.42295
1981	2.3575
1982	2.29261
1983	2.23087
1984	2.18978
1985	2.14534
1986	2.11727
1987	2.08051
1988	2.01014
1989	1.89968
1990	1.76996
1991	1.58231
1992	1.0229
1993	0.9215
1994	0.87011
1995	0.82423
1996	0.78577
1997	0.75235
1998	0.7384
1999	0.77228
2000	0.82381
2001	0.88013
2002	0.94699
2003	0.98997
2004	0.99409
2005	0.97257
2006	0.95546
2007	0.93106
2008	0.91297
2009	0.88398
2010	0.86129
2011	0.82614
2012	0.7918
2013	0.79288
2014	0.8373
2015	0.88952
2016	0.97048
2017	1.02795