Year	Percent change (Units)
1981	20.670
1982	21.759
1983	17.871
1984	9.677
1985	5.882
1986	11.111
1987	3.750
1988	3.614
1989	4.651
1990	11.111
1991	10.614
1992	13.910
1993	4.373
1994	3.946
1995	5.706
1996	9.106
1997	0.395
1998	8.362
1999	-1.569
2000	-1.032
2001	4.562
2002	2.983
2003	-2.281
2004	-0.298
2005	1.759
2006	5.813
2007	3.360
2008	6.646
2009	-0.311
2010	3.440
2011	3.534
2012	4.140
2013	0.065
2014	-0.339
2015	-0.525
2016	-0.250
2017	0.269
2018	1.003
2019	1.936
2020	-0.853
2021	5.375
2022	7.577
2023	1.332
2024	2.000
2025	2.000
2026	2.000
2027	2.000
2028	2.000
2029	2.000