Year	Percent
1960	2.43774
1961	2.45311
1962	2.44288
1963	2.4207
1964	2.36568
1965	2.23784
1966	2.14251
1967	2.03978
1968	1.94435
1969	1.81783
1970	1.7424
1971	1.64146
1972	1.52413
1973	1.46581
1974	1.43727
1975	1.44048
1976	1.45397
1977	1.47715
1978	1.4886
1979	1.45309
1980	1.41374
1981	1.3292
1982	1.30028
1983	1.38239
1984	1.60122
1985	1.95324
1986	2.3395
1987	2.62557
1988	2.69452
1989	2.51803
1990	2.16659
1991	1.76308
1992	1.44006
1993	1.26258
1994	1.24944
1995	1.37177
1996	1.50287
1997	1.6054
1998	1.68923
1999	1.72146
2000	1.72076
2001	1.70563
2002	1.71481
2003	1.7613
2004	1.83579
2005	1.95011
2006	2.0742
2007	2.15256
2008	2.18647
2009	2.13869
2010	2.05105
2011	1.93342
2012	1.85267
2013	1.78672
2014	1.75627
2015	1.74909
2016	1.75312
2017	1.7358