Year	Percent (Units)
1980	7.951
1981	8.117
1982	8.351
1983	8.451
1984	8.450
1985	8.578
1986	8.565
1987	8.636
1988	8.812
1989	8.918
1990	8.988
1991	9.082
1992	8.249
1993	8.054
1994	7.908
1995	7.828
1996	7.773
1997	7.544
1998	7.246
1999	6.979
2000	6.844
2001	6.707
2002	6.527
2003	6.369
2004	6.181
2005	6.011
2006	5.790
2007	5.580
2008	5.355
2009	5.072
2010	5.017
2011	4.830
2012	4.756
2013	4.742
2014	4.582
2015	4.636
2016	4.429
2017	4.277
2018	4.157
2019	4.029
2020	3.977
2021	3.833
2022	3.744
2023	3.702
2024	3.620
2025	3.543
2026	3.463
2027	3.378
2028	3.297
2029	3.213