Year	Percent
1961	21.84557
1962	21.98009
1963	22.11461
1964	22.16842
1965	22.30293
1966	22.43745
1967	22.4509
1968	22.58542
1969	22.69303
1970	22.65268
1971	23.04278
1972	23.44633
1973	23.71536
1974	24.0113
1975	24.29379
1976	24.57627
1977	24.87221
1978	24.88566
1979	24.91256
1980	24.95292
1981	25.31612
1982	25.74657
1983	26.10977
1984	26.44606
1985	26.83616
1986	27.17245
1987	27.50874
1988	27.84504
1989	28.24859
1990	28.57143
1991	28.70595
1992	28.92117
1993	28.92117
1994	28.7194
1995	28.67904
1996	28.67904
1997	28.78666
1998	28.90772
1999	29.01533
2000	29.99731
2001	30.13721
2002	30.10223
2003	30.06726
2004	30.03228
2005	29.99731
2006	29.92198
2007	30.02152
2008	29.98655
2009	30.01883
2010	30.48682
2011	30.44122
2012	30.3067
2013	30.17218
2014	30.12682
2015	29.99191
2016	29.85699
2017	29.72207
2018	29.56322
2019	29.42842
2020	29.30844
2021	29.40572