Year	Percent change (Units)
1980	18.074
1981	9.406
1982	9.023
1983	8.213
1984	4.726
1985	3.363
1986	4.353
1987	2.487
1988	4.491
1989	9.850
1990	23.323
1991	33.949
1992	8.741
1993	10.775
1994	21.769
1995	29.432
1996	23.845
1997	20.200
1998	13.668
1999	11.664
2000	11.048
2001	9.666
2002	7.702
2003	7.671
2004	8.114
2005	8.809
2006	5.578
2007	6.936
2008	11.403
2009	5.496
2010	4.699
2011	6.762
2012	5.196
2013	5.162
2014	6.129
2015	3.158
2016	2.725
2017	3.934
2018	4.347
2019	4.366
2020	3.468
2021	4.481
2022	9.090
2023	6.663
2024	4.390
2025	4.147
2026	4.000
2027	4.000
2028	4.000
2029	4.000