Year	Percent
1960	36.57463
1961	38.68081
1962	36.62203
1963	43.10511
1964	46.53238
1965	37.52706
1966	34.3964
1967	30.20706
1968	28.15878
1969	27.40995
1970	26.48573
1971	27.13787
1972	26.50608
1973	24.60695
1974	24.17204
1975	24.48594
1976	23.04668
1977	21.78997
1978	19.91691
1979	18.53634
1980	14.26932
1981	15.02543
1982	14.00327
1983	12.62528
1984	11.87256
1985	11.7537
1986	10.42823
1987	9.30921
1988	9.22102
1989	8.54152
1990	7.6065
1991	6.82449
1992	6.60761
1993	5.91488
1994	5.65822
1995	5.32867
1996	4.96065
1997	4.47517
1998	4.22594
1999	4.24975
2000	3.85779
2001	3.56582
2002	3.2068
2003	2.9646
2004	2.95802
2005	2.61998
2006	2.49747
2007	2.28341
2008	2.14225
2009	2.24056
2010	2.14402
2011	2.2092
2012	2.18619
2013	2.09905
2014	2.05668
2015	2.00391
2016	1.85903
2017	1.85076
2018	1.7464
2019	1.66793
2020	1.76572
2021	1.85566
2022	1.64165