Year	Percent change (Units)
1981	3.108
1982	18.428
1983	1.792
1984	5.924
1985	-1.898
1986	2.362
1987	2.895
1988	2.293
1989	0.728
1990	6.048
1991	21.408
1992	14.495
1993	7.536
1994	42.351
1995	40.700
1996	8.743
1997	16.606
1998	-5.956
1999	1.967
2000	5.924
2001	-0.219
2002	6.165
2003	7.677
2004	10.250
2005	5.608
2006	12.138
2007	6.579
2008	22.323
2009	5.737
2010	0.237
2011	8.274
2012	3.930
2013	3.571
2014	2.130
2015	4.568
2016	7.312
2017	0.626
2018	1.137
2019	6.696
2020	3.749
2021	1.885
2022	21.665
2023	6.423
2024	5.400
2025	5.000
2026	5.000
2027	5.000
2028	5.000
2029	5.000