Year	Percent change (Units)
1980	18.017
1981	12.244
1982	9.481
1983	11.787
1984	10.475
1985	4.705
1986	5.821
1987	9.250
1988	8.072
1989	6.407
1990	7.800
1991	9.435
1992	7.546
1993	9.664
1994	8.528
1995	9.415
1996	7.981
1997	6.237
1998	58.447
1999	20.470
2000	3.688
2001	11.466
2002	11.908
2003	6.791
2004	6.062
2005	10.464
2006	13.099
2007	6.319
2008	9.871
2009	4.804
2010	5.137
2011	5.345
2012	3.979
2013	6.410
2014	6.399
2015	6.360
2016	3.530
2017	3.807
2018	3.291
2019	2.822
2020	2.031
2021	1.561
2022	4.139
2023	3.713
2024	2.557
2025	2.587
2026	2.533
2027	2.518
2028	2.513
2029	2.512