Year	Percent change (Units)
1981	15.546
1982	12.909
1983	4.856
1984	6.994
1985	7.067
1986	2.805
1987	1.204
1988	8.283
1989	14.366
1990	10.440
1991	8.567
1992	6.379
1993	14.987
1994	5.988
1995	6.017
1996	7.449
1997	5.066
1998	9.047
1999	4.890
2000	4.757
2001	4.983
2002	5.133
2003	3.912
2004	5.601
2005	3.913
2006	11.883
2007	8.617
2008	6.779
2009	1.472
2010	6.177
2011	4.810
2012	3.179
2013	4.063
2014	0.239
2015	1.281
2016	2.325
2017	4.271
2018	1.760
2019	0.879
2020	2.711
2021	6.766
2022	12.193
2023	3.854
2024	5.074
2025	3.952
2026	3.590
2027	3.459
2028	3.532
2029	3.503