Year	Percent change (Units)
1980	11.515
1981	9.151
1982	8.786
1983	7.830
1984	3.659
1985	4.247
1986	3.175
1987	2.923
1988	6.726
1989	11.391
1990	36.421
1991	21.212
1992	6.429
1993	13.087
1994	29.080
1995	26.667
1996	25.408
1997	12.735
1998	15.661
1999	10.988
2000	10.100
2001	8.810
2002	8.097
2003	6.795
2004	9.183
2005	7.748
2006	5.286
2007	8.873
2008	10.831
2009	2.951
2010	6.485
2011	5.605
2012	5.391
2013	4.917
2014	5.820
2015	2.357
2016	3.315
2017	4.728
2018	4.224
2019	4.084
2020	4.013
2021	5.316
2022	9.796
2023	5.190
2024	4.300
2025	4.000
2026	4.000
2027	4.000
2028	4.000
2029	4.000