Year	Percent change (Units)
1980	18.200
1981	20.056
1982	10.807
1983	11.568
1984	12.940
1985	20.463
1986	13.737
1987	13.377
1988	20.395
1989	7.546
1990	13.092
1991	8.934
1992	7.558
1993	12.023
1994	13.769
1995	12.289
1996	6.425
1997	7.945
1998	7.510
1999	5.862
2000	9.911
2001	7.489
2002	11.869
2003	7.276
2004	3.470
2005	4.895
2006	5.195
2007	8.076
2008	12.657
2009	7.448
2010	4.509
2011	6.107
2012	8.940
2013	5.621
2014	5.681
2015	4.951
2016	7.847
2017	6.221
2018	4.815
2019	2.598
2020	3.872
2021	3.719
2022	4.802
2023	4.949
2024	3.881
2025	3.054
2026	2.977
2027	2.972
2028	2.972
2029	2.972