Year	Percent
1961	18.77918
1962	19.2227
1963	19.66622
1964	20.10974
1965	20.55326
1966	20.99678
1967	21.4403
1968	21.88382
1969	22.32734
1970	22.77157
1971	23.19104
1972	23.61052
1973	24.02999
1974	24.44946
1975	24.86905
1976	25.45782
1977	26.04658
1978	26.63535
1979	27.22412
1980	27.81925
1981	28.04617
1982	28.27311
1983	28.50005
1984	28.72699
1985	28.95366
1986	28.78382
1987	28.61395
1988	28.44408
1989	28.27421
1990	28.10434
1991	27.93447
1992	27.7646
1993	27.59473
1994	27.42486
1995	27.25547
1996	27.26787
1997	27.28028
1998	27.29269
1999	27.30509
2000	27.3175
2001	27.32991
2002	27.34232
2003	27.35472
2004	27.36713
2005	27.37954
2006	27.39258
2007	27.47882
2008	27.56506
2009	27.6513
2010	27.73753
2011	27.82377
2012	27.91001
2013	27.99625
2014	28.08249
2015	28.16873
2016	28.25497
2017	28.34107
2018	28.41563
2019	28.49013
2020	28.56462
2021	28.63909