Year	Percent
1961	15.88712
1962	16.01405
1963	16.11982
1964	16.24675
1965	16.37368
1966	16.5006
1967	16.64869
1968	16.75446
1969	16.86023
1970	16.87716
1971	16.98293
1972	17.12466
1973	17.26217
1974	17.51602
1975	17.7593
1976	18.00258
1977	18.28605
1978	18.34317
1979	18.853
1980	18.89107
1981	18.95454
1982	19.06031
1983	19.16608
1984	19.27186
1985	19.37763
1986	19.52571
1987	19.4834
1988	19.4834
1989	19.44109
1990	19.39879
1991	19.35648
1992	19.37763
1993	19.37763
1994	19.37763
1995	19.37763
1996	19.37763
1997	19.37763
1998	19.37763
1999	19.37763
2000	19.37763
2001	19.37763
2002	19.37763
2003	19.37763
2004	19.4834
2005	19.48975
2006	19.48975
2007	19.48975
2008	19.59552
2009	19.7013
2010	20.51998
2011	20.62575
2012	20.62575
2013	20.62575
2014	20.62575
2015	20.62575
2016	20.62575
2017	20.62575
2018	20.62575
2019	20.62575
2020	20.62575
2021	20.62575