Year	Percent (Units)
1980	3.228
1981	3.465
1982	3.449
1983	3.212
1984	3.185
1985	3.133
1986	2.910
1987	2.861
1988	2.771
1989	2.769
1990	2.802
1991	2.844
1992	2.651
1993	2.675
1994	2.712
1995	2.462
1996	2.517
1997	2.593
1998	2.679
1999	2.661
2000	2.667
2001	2.591
2002	2.515
2003	2.445
2004	2.405
2005	2.346
2006	2.337
2007	2.265
2008	2.221
2009	2.091
2010	2.085
2011	2.076
2012	2.084
2013	2.030
2014	2.052
2015	2.059
2016	2.110
2017	2.070
2018	2.039
2019	1.979
2020	1.862
2021	1.851
2022	1.861
2023	1.864
2024	1.850
2025	1.818
2026	1.797
2027	1.779
2028	1.761
2029	1.744