Year	Percent
1960	3.54796
1961	2.99481
1962	2.8895
1963	2.9113
1964	2.92397
1965	2.93172
1966	2.93298
1967	2.93413
1968	2.94367
1969	2.96421
1970	2.96998
1971	2.90337
1972	2.91911
1973	2.9084
1974	2.86563
1975	2.80337
1976	2.73016
1977	2.66747
1978	2.63219
1979	2.63288
1980	2.68681
1981	2.90477
1982	2.91677
1983	2.89068
1984	2.80917
1985	2.93644
1986	3.30273
1987	3.18669
1988	3.13069
1989	3.15924
1990	3.23396
1991	3.29754
1992	3.28804
1993	3.26651
1994	3.15255
1995	2.97554
1996	2.78599
1997	2.62575
1998	2.48842
1999	2.39199
2000	2.32229
2001	2.2608
2002	2.29243
2003	2.2572
2004	2.18015
2005	2.09726
2006	2.0127
2007	1.94627
2008	1.93041
2009	1.96994
2010	2.05423
2011	2.15246
2012	2.23077
2013	2.26097
2014	2.2362
2015	2.16791
2016	2.08958
2017	2.02085