Year	Percent change (Units)
1980	18.201
1981	13.083
1982	8.979
1983	5.252
1984	46.673
1985	23.215
1986	-0.325
1987	3.042
1988	12.230
1989	11.367
1990	13.201
1991	19.351
1992	8.582
1993	6.757
1994	12.489
1995	6.908
1996	8.294
1997	5.598
1998	9.369
1999	6.200
2000	6.545
2001	5.396
2002	2.757
2003	2.223
2004	4.799
2005	6.640
2006	5.448
2007	2.914
2008	8.211
2009	4.240
2010	3.738
2011	4.745
2012	3.158
2013	2.592
2014	3.594
2015	0.690
2016	1.234
2017	2.853
2018	5.310
2019	2.392
2020	2.393
2021	3.927
2022	5.821
2023	5.978
2024	3.583
2025	2.954
2026	3.000
2027	3.000
2028	3.000
2029	3.000