Year	Percent
1961	19.0915
1962	18.85176
1963	18.68802
1964	18.54275
1965	18.54401
1966	18.54401
1967	18.57927
1968	18.55912
1969	18.55912
1970	18.56458
1971	19.07555
1972	19.06001
1973	18.60153
1974	18.61496
1975	18.37018
1976	18.48271
1977	18.40335
1978	18.40797
1979	18.39831
1980	18.40251
1981	16.44638
1982	16.41951
1983	16.49298
1984	16.6307
1985	16.396
1986	16.24359
1987	16.28179
1988	16.29775
1989	16.27382
1990	16.23855
1991	16.21588
1992	16.3179
1993	16.31664
1994	16.64329
1995	16.64707
1996	16.64161
1997	16.66429
1998	16.72139
1999	16.6815
2000	16.80326
2001	16.84021
2002	16.73356
2003	16.75485
2004	17.27519
2005	17.3029
2006	17.2903
2007	17.32011
2008	17.34404
2009	17.37385
2010	17.37133
2011	17.37721
2012	17.38149
2013	17.39553
2014	17.39527
2015	17.40592
2016	17.36553
2017	17.35501
2018	17.35657
2019	17.347
2020	17.347
2021	17.347