Year	Percent (Units)
1980	0.587
1981	0.588
1982	0.591
1983	0.586
1984	0.580
1985	0.578
1986	0.591
1987	0.600
1988	0.597
1989	0.596
1990	0.597
1991	0.597
1992	0.560
1993	0.581
1994	0.593
1995	0.602
1996	0.592
1997	0.588
1998	0.576
1999	0.533
2000	0.523
2001	0.519
2002	0.518
2003	0.517
2004	0.517
2005	0.516
2006	0.524
2007	0.531
2008	0.532
2009	0.541
2010	0.537
2011	0.553
2012	0.549
2013	0.559
2014	0.569
2015	0.562
2016	0.577
2017	0.571
2018	0.565
2019	0.567
2020	0.542
2021	0.565
2022	0.586
2023	0.572
2024	0.561
2025	0.557
2026	0.556
2027	0.556
2028	0.555
2029	0.555