Year	Percent
1961	40.08485
1962	40.09415
1963	40.10439
1964	40.11788
1965	40.12765
1966	40.13788
1967	40.14718
1968	40.16393
1969	40.18021
1970	40.20115
1971	40.22301
1972	40.24627
1973	40.27092
1974	40.30349
1975	40.32395
1976	40.35466
1977	40.37978
1978	40.40397
1979	40.42862
1980	40.45327
1981	40.477
1982	40.50258
1983	40.59655
1984	42.99364
1985	45.41352
1986	47.81154
1987	50.2305
1988	52.62619
1989	55.02654
1990	57.44131
1991	57.53016
1992	57.56458
1993	60.839
1994	64.09529
1995	67.35157
1996	70.60786
1997	73.86414
1998	77.58561
1999	80.84189
2000	80.84189
2001	80.84468
2002	80.84561
2003	80.84794
2004	80.80653
2005	80.81026
2006	80.79025
2007	80.79072
2008	80.7428
2009	80.67907
2010	80.66558
2011	80.65721
2012	80.63721
2013	80.61395
2014	80.74434
2015	80.77304
2016	80.76839
2017	80.75402
2018	80.75374
2019	80.76348
2020	80.77321
2021	80.77304