Year	Percent
1961	15.95924
1962	16.02044
1963	16.07706
1964	16.24996
1965	16.19335
1966	16.43358
1967	16.47489
1968	16.47642
1969	16.47489
1970	16.52691
1971	16.53304
1972	16.53304
1973	15.79398
1974	15.81081
1975	15.83224
1976	15.85519
1977	15.84601
1978	15.86284
1979	15.87814
1980	15.89038
1981	15.94547
1982	15.97607
1983	15.97148
1984	15.947
1985	15.95771
1986	15.96689
1987	15.947
1988	15.87202
1989	15.90568
1990	15.95618
1991	15.93782
1992	15.91027
1993	15.98372
1994	15.94547
1995	15.98984
1996	16.07247
1997	16.09542
1998	16.08624
1999	16.23313
2000	16.54375
2001	16.73807
2002	16.71665
2003	16.80387
2004	16.96
2005	17.23858
2006	17.7468
2007	18.33762
2008	18.792
2009	19.04332
2010	19.1746
2011	19.2227
2012	19.21304
2013	19.27329
2014	19.34219
2015	19.52134
2016	19.54717
2017	19.99786
2018	20.02651
2019	19.88571
2020	19.88754
2021	19.88754