Year	Percent
1960	2.37095
1961	2.41572
1962	2.46058
1963	2.49866
1964	2.53008
1965	2.56262
1966	2.57301
1967	2.58558
1968	2.63662
1969	2.73913
1970	2.86055
1971	3.00084
1972	3.09575
1973	3.07938
1974	2.92677
1975	2.69435
1976	2.4739
1977	2.31161
1978	2.19499
1979	2.13805
1980	2.14051
1981	2.10977
1982	2.11447
1983	2.31268
1984	2.74178
1985	3.2905
1986	3.86829
1987	4.29631
1988	4.45401
1989	4.29649
1990	3.94764
1991	3.54484
1992	3.22106
1993	3.01041
1994	2.95187
1995	2.98243
1996	3.04201
1997	3.0304
1998	2.88974
1999	2.58837
2000	2.19395
2001	1.79187
2002	1.46578
2003	1.23526
2004	1.13587
2005	1.13664
2006	1.1516
2007	1.16941
2008	1.26414
2009	1.44532
2010	1.67652
2011	1.93458
2012	2.15713
2013	2.29621
2014	2.32424
2015	2.27544
2016	2.208
2017	2.1575