Year	Percent (Units)
1980	4.254
1981	3.983
1982	3.991
1983	3.764
1984	3.796
1985	3.955
1986	4.111
1987	4.103
1988	3.936
1989	3.918
1990	3.609
1991	3.559
1992	3.189
1993	3.274
1994	3.349
1995	3.374
1996	3.320
1997	3.299
1998	3.220
1999	3.127
2000	3.115
2001	3.083
2002	3.090
2003	3.004
2004	3.017
2005	2.974
2006	2.938
2007	2.960
2008	3.022
2009	3.031
2010	3.097
2011	3.099
2012	2.971
2013	2.959
2014	2.901
2015	2.687
2016	2.523
2017	2.460
2018	2.418
2019	2.382
2020	2.372
2021	2.336
2022	2.328
2023	2.324
2024	2.302
2025	2.278
2026	2.254
2027	2.230
2028	2.207
2029	2.185