Year	Percent
1961	19.92975
1962	20.01473
1963	20.06571
1964	20.36596
1965	20.54725
1966	20.54725
1967	20.55858
1968	20.26399
1969	19.69748
1970	19.36891
1971	13.87945
1972	13.87945
1973	13.87945
1974	14.1627
1975	14.1627
1976	14.44596
1977	14.44596
1978	14.72921
1979	14.72921
1980	15.01246
1981	15.01246
1982	15.18242
1983	15.23907
1984	15.24473
1985	16.93859
1986	18.63811
1987	20.9608
1988	23.51008
1989	25.12463
1990	25.23793
1991	25.54951
1992	25.57784
1993	25.66848
1994	25.88942
1995	25.88942
1996	25.94607
1997	25.94607
1998	26.22932
1999	26.28597
2000	27.02243
2001	27.70224
2002	28.3254
2003	28.89191
2004	29.62837
2005	30.34217
2006	30.33651
2007	30.33651
2008	30.33651
2009	30.33651
2010	30.60843
2011	30.87862
2012	31.34133
2013	31.56653
2014	31.73508
2015	31.99427
2016	32.29311
2017	32.76757
2018	33.17405
2019	33.71083
2020	34.24761
2021	34.55212