Year	Percent (Units)
1980	0.726
1981	0.732
1982	0.776
1983	0.798
1984	0.807
1985	0.823
1986	0.794
1987	0.760
1988	0.713
1989	0.721
1990	0.698
1991	0.674
1992	0.616
1993	0.591
1994	0.569
1995	0.570
1996	0.570
1997	0.554
1998	0.566
1999	0.565
2000	0.559
2001	0.562
2002	0.577
2003	0.590
2004	0.586
2005	0.590
2006	0.576
2007	0.565
2008	0.562
2009	0.571
2010	0.569
2011	0.564
2012	0.535
2013	0.515
2014	0.515
2015	0.481
2016	0.457
2017	0.442
2018	0.433
2019	0.425
2020	0.416
2021	0.406
2022	0.407
2023	0.411
2024	0.414
2025	0.413
2026	0.411
2027	0.407
2028	0.403
2029	0.400