Year	Percent
1961	20.12026
1962	20.24602
1963	20.37177
1964	20.26888
1965	20.39463
1966	20.40606
1967	20.53182
1968	20.54325
1969	20.55468
1970	20.56154
1971	20.57526
1972	20.94337
1973	20.96623
1974	21.21773
1975	21.22917
1976	21.22917
1977	21.22917
1978	21.46695
1979	21.58127
1980	21.58127
1981	21.58127
1982	21.60642
1983	21.60642
1984	21.60642
1985	21.64072
1986	21.67501
1987	21.67501
1988	21.78933
1989	21.10341
1990	21.10341
1991	22.01797
1992	21.83506
1993	22.56671
1994	21.37778
1995	20.80618
1996	20.80618
1997	19.80017
1998	19.77731
1999	19.43435
2000	19.43435
2001	19.41148
2002	19.86876
2003	19.86876
2004	19.86876
2005	20.21172
2006	20.55468
2007	20.89764
2008	18.72556
2009	18.07423
2010	18.92614
2011	19.68595
2012	19.72854
2013	20.41737
2014	21.35085
2015	21.35085
2016	21.44298
2017	21.48905
2018	21.53512
2019	21.58119
2020	21.74244
2021	21.70788