Year	Percent (Units)
1980	0.617
1981	0.648
1982	0.699
1983	0.774
1984	0.819
1985	0.853
1986	0.918
1987	0.997
1988	1.068
1989	1.103
1990	1.165
1991	1.260
1992	1.204
1993	1.262
1994	1.340
1995	1.417
1996	1.471
1997	1.501
1998	1.386
1999	1.493
2000	1.554
2001	1.590
2002	1.666
2003	1.652
2004	1.650
2005	1.644
2006	1.645
2007	1.653
2008	1.654
2009	1.674
2010	1.699
2011	1.696
2012	1.669
2013	1.631
2014	1.631
2015	1.724
2016	1.740
2017	1.716
2018	1.705
2019	1.697
2020	1.735
2021	1.701
2022	1.689
2023	1.660
2024	1.647
2025	1.633
2026	1.619
2027	1.603
2028	1.588
2029	1.572