Year	Percent
1961	19.38915
1962	19.41642
1963	19.14371
1964	19.17098
1965	19.10008
1966	18.80556
1967	18.6474
1968	18.53559
1969	18.14017
1970	18.26016
1971	17.84292
1972	17.65139
1973	17.51773
1974	17.39498
1975	17.25239
1976	17.11596
1977	17.03057
1978	16.94323
1979	16.8559
1980	16.79498
1981	16.70579
1982	16.64118
1983	16.57291
1984	16.56978
1985	16.50027
1986	16.41075
1987	16.3412
1988	16.25069
1989	16.12178
1990	15.99561
1991	15.86396
1992	15.73231
1993	15.59517
1994	15.42787
1995	15.25507
1996	15.08916
1997	14.91632
1998	14.74897
1999	14.59808
2000	14.42524
2001	14.30178
2002	14.19753
2003	14.10151
2004	14.0192
2005	13.9369
2006	13.86392
2007	13.79095
2008	13.71523
2009	13.64774
2010	13.58848
2011	13.4952
2012	13.45679
2013	13.42112
2014	13.36077
2015	13.29492
2016	13.20439
2017	13.10837
2018	13.02058
2019	12.93553
2020	12.84499
2021	12.78189