Year	Percent (Units)
1980	3.114
1981	3.109
1982	2.455
1983	2.012
1984	1.837
1985	1.600
1986	1.810
1987	1.628
1988	1.762
1989	1.691
1990	1.872
1991	2.102
1992	1.967
1993	1.903
1994	1.859
1995	1.797
1996	1.776
1997	1.725
1998	1.727
1999	1.606
2000	1.619
2001	1.561
2002	1.476
2003	1.578
2004	1.618
2005	1.632
2006	1.594
2007	1.541
2008	1.591
2009	1.565
2010	1.562
2011	1.669
2012	1.670
2013	1.602
2014	1.589
2015	1.406
2016	1.308
2017	1.325
2018	1.320
2019	1.299
2020	1.290
2021	1.274
2022	1.325
2023	1.275
2024	1.268
2025	1.302
2026	1.313
2027	1.318
2028	1.317
2029	1.323