Year	Percent
1960	1.90352
1961	1.92775
1962	1.94577
1963	1.93069
1964	1.8703
1965	1.7888
1966	1.7018
1967	1.6539
1968	1.68174
1969	1.80526
1970	1.99349
1971	2.20225
1972	2.39013
1973	2.54837
1974	2.6625
1975	2.74667
1976	2.80467
1977	2.86935
1978	2.97056
1979	3.11906
1980	3.28266
1981	3.46243
1982	3.58731
1983	3.58151
1984	3.42219
1985	3.1767
1986	2.89843
1987	2.68526
1988	2.60174
1989	2.68442
1990	2.86872
1991	3.09029
1992	3.25162
1993	3.30219
1994	3.21236
1995	3.0432
1996	2.85527
1997	2.73231
1998	2.71538
1999	2.83256
2000	3.03294
2001	3.24549
2002	3.41152
2003	3.5263
2004	3.57396
2005	3.5759
2006	3.56616
2007	3.56454
2008	3.56345
2009	3.56682
2010	3.5701
2011	3.57035
2012	3.5595
2013	3.53182
2014	3.48541
2015	3.42802
2016	3.36757
2017	3.31351