Year	Percent (Units)
1980	2.152
1981	2.181
1982	2.104
1983	2.107
1984	2.137
1985	2.161
1986	2.133
1987	2.138
1988	2.136
1989	2.108
1990	2.031
1991	1.941
1992	1.763
1993	1.775
1994	1.801
1995	1.784
1996	1.747
1997	1.751
1998	1.770
1999	1.798
2000	1.804
2001	1.794
2002	1.798
2003	1.759
2004	1.722
2005	1.698
2006	1.656
2007	1.605
2008	1.574
2009	1.535
2010	1.504
2011	1.493
2012	1.455
2013	1.467
2014	1.476
2015	1.422
2016	1.441
2017	1.448
2018	1.437
2019	1.425
2020	1.393
2021	1.379
2022	1.385
2023	1.358
2024	1.331
2025	1.320
2026	1.304
2027	1.286
2028	1.268
2029	1.251