Year	Percent
1975	42.40755
1976	39.97063
1977	38.02104
1978	35.70262
1979	36.2318
1980	33.4026
1981	33.81829
1982	32.73577
1983	31.08394
1984	32.50878
1985	31.86121
1986	32.9344
1987	32.75119
1988	31.64532
1989	30.43673
1990	29.91315
1991	30.6548
1992	32.78561
1993	34.11019
1994	21.53735
1995	20.70422
1996	20.30945
1997	20.21347
1998	21.26126
1999	22.38407
2000	19.63692
2001	18.28744
2002	18.10623
2003	19.16298
2004	20.24978
2005	17.76224
2006	15.7719
2007	16.70802
2008	14.7437
2009	15.51453
2010	16.44002
2011	17.0495
2012	16.64427
2013	17.10784
2014	16.35534
2015	16.8686
2016	16.61762
2017	16.8054
2018	17.0723
2019	19.63512
2020	17.81157
2021	16.32325