Year	Percent
1961	10.40164
1962	10.24207
1963	9.77317
1964	9.67988
1965	9.44912
1966	9.32146
1967	9.292
1968	9.13488
1969	9.1938
1970	9.21344
1971	9.22572
1972	9.1668
1973	9.12752
1974	9.16925
1975	9.14716
1976	9.16925
1977	9.13734
1978	9.15207
1979	9.11033
1980	9.09315
1981	9.02195
1982	8.98513
1983	8.92621
1984	8.86484
1985	8.57761
1986	8.53342
1987	8.48186
1988	8.43767
1989	8.39103
1990	8.37876
1991	8.24373
1992	8.20936
1993	8.23882
1994	8.23882
1995	8.02033
1996	8.09398
1997	8.00069
1998	7.93195
1999	7.84112
2000	7.30128
2001	7.49718
2002	7.70831
2003	7.68081
2004	7.74096
2005	7.8588
2006	7.73335
2007	7.66166
2008	7.55095
2009	7.52983
2010	7.54579
2011	7.51977
2012	7.44219
2013	7.45344
2014	7.45341
2015	7.43499
2016	7.41675
2017	7.3933
2018	7.36634
2019	7.37761
2020	7.37948
2021	7.37302