Year	Percent
1961	26.20438
1962	26.43846
1963	26.69016
1964	26.9771
1965	27.24138
1966	27.5107
1967	27.71961
1968	27.91593
1969	28.12233
1970	28.32872
1971	28.53763
1972	28.74402
1973	28.9479
1974	29.44626
1975	29.95721
1976	30.46564
1977	30.94891
1978	31.45985
1979	31.94312
1980	32.45155
1981	32.96501
1982	33.26202
1983	33.56154
1984	33.86106
1985	34.16058
1986	34.48528
1987	34.7848
1988	35.08432
1989	35.38384
1990	35.58915
1991	35.79195
1992	36.16949
1993	36.16949
1994	36.54704
1995	36.92459
1996	36.92459
1997	36.92459
1998	37.55636
1999	37.81057
2000	37.99431
2001	38.22084
2002	38.49268
2003	38.6739
2004	38.90043
2005	39.12696
2006	39.35349
2007	39.58002
2008	39.82416
2009	40.07838
2010	40.38545
2011	40.75545
2012	41.35449
2013	41.6666
2014	42.11714
2015	42.63312
2016	42.11966
2017	42.09197
2018	42.3034
2019	42.30843
2020	42.30843
2021	42.30843