Year	Percent
1960	2.41937
1961	2.51404
1962	2.62558
1963	2.75914
1964	2.91424
1965	3.07448
1966	3.23481
1967	3.36696
1968	3.44143
1969	3.44818
1970	3.40901
1971	3.35039
1972	3.29859
1973	3.26066
1974	3.24451
1975	3.23797
1976	3.23004
1977	3.20256
1978	3.14544
1979	3.05347
1980	2.93994
1981	2.83907
1982	2.75089
1983	2.64831
1984	2.52891
1985	2.40994
1986	2.28476
1987	2.19563
1988	2.19582
1989	2.30559
1990	2.48535
1991	2.6756
1992	2.83238
1993	2.9558
1994	3.03227
1995	3.0709
1996	3.10592
1997	3.1328
1998	3.1168
1999	3.05296
2000	2.95975
2001	2.87045
2002	2.79602
2003	2.72261
2004	2.65294
2005	2.59486
2006	2.52081
2007	2.46952
2008	2.50782
2009	2.65492
2010	2.86233
2011	3.08668
2012	3.25442
2013	3.32037
2014	3.26041
2015	3.12045
2016	2.96516
2017	2.84091