Year	Percent change (Units)
1981	4.126
1982	12.731
1983	15.385
1984	24.681
1985	25.455
1986	52.301
1987	15.317
1988	12.418
1989	8.394
1990	10.487
1991	11.553
1992	4.246
1993	5.128
1994	5.043
1995	4.039
1996	2.253
1997	0.309
1998	4.779
1999	1.749
2000	0.203
2001	8.069
2002	13.005
2003	17.564
2004	8.090
2005	4.846
2006	0.423
2007	6.020
2008	6.835
2009	2.718
2010	5.789
2011	4.382
2012	4.908
2013	5.575
2014	6.950
2015	6.667
2016	7.875
2017	6.945
2018	6.411
2019	7.675
2020	5.665
2021	7.607
2022	13.739
2023	17.300
2024	12.945
2025	8.100
2026	5.000
2027	5.000
2028	5.000
2029	5.000