Year	Percent (Units)
1980	2.258
1981	2.324
1982	2.523
1983	2.729
1984	3.011
1985	3.300
1986	3.473
1987	3.738
1988	3.976
1989	3.997
1990	3.991
1991	4.246
1992	4.368
1993	4.879
1994	5.356
1995	5.734
1996	6.068
1997	6.371
1998	6.685
1999	6.957
2000	7.201
2001	7.614
2002	8.082
2003	8.545
2004	8.937
2005	9.509
2006	10.184
2007	11.049
2008	11.764
2009	12.932
2010	13.591
2011	14.331
2012	14.998
2013	15.370
2014	15.654
2015	15.939
2016	16.053
2017	16.148
2018	16.645
2019	17.161
2020	18.069
2021	18.418
2022	18.351
2023	18.734
2024	19.007
2025	19.169
2026	19.288
2027	19.376
2028	19.436
2029	19.484