Year	Percent change (Units)
1981	12.500
1982	19.136
1983	10.363
1984	11.268
1985	19.831
1986	12.676
1987	9.062
1988	15.759
1989	12.129
1990	17.660
1991	16.510
1992	15.298
1993	6.145
1994	10.658
1995	9.275
1996	8.814
1997	7.300
1998	8.947
1999	6.330
2000	6.999
2001	10.906
2002	7.719
2003	5.163
2004	3.693
2005	5.102
2006	5.930
2007	10.650
2008	10.541
2009	3.547
2010	3.612
2011	7.182
2012	4.969
2013	5.504
2014	2.012
2015	7.481
2016	4.443
2017	4.835
2018	5.235
2019	3.985
2020	6.453
2021	7.204
2022	6.842
2023	6.633
2024	5.600
2025	5.250
2026	5.250
2027	5.000
2028	5.061
2029	5.061