Year	Percent (Units)
1980	2.195
1981	2.141
1982	2.159
1983	2.143
1984	2.087
1985	2.063
1986	2.062
1987	2.101
1988	2.116
1989	2.143
1990	2.139
1991	2.141
1992	1.943
1993	1.881
1994	1.870
1995	1.878
1996	1.852
1997	1.848
1998	1.879
1999	1.902
2000	1.907
2001	1.934
2002	1.933
2003	1.913
2004	1.874
2005	1.855
2006	1.835
2007	1.805
2008	1.770
2009	1.711
2010	1.628
2011	1.554
2012	1.470
2013	1.428
2014	1.419
2015	1.446
2016	1.488
2017	1.504
2018	1.485
2019	1.474
2020	1.348
2021	1.348
2022	1.380
2023	1.372
2024	1.355
2025	1.340
2026	1.323
2027	1.304
2028	1.286
2029	1.269