Year	Percent change (Units)
1981	3.802
1982	2.376
1983	4.016
1984	5.181
1985	3.223
1986	4.249
1987	3.732
1988	2.159
1989	2.612
1990	5.941
1991	3.339
1992	5.040
1993	4.574
1994	4.085
1995	4.925
1996	4.622
1997	4.490
1998	5.177
1999	4.670
2000	5.293
2001	5.077
2002	3.833
2003	4.740
2004	5.240
2005	6.536
2006	6.672
2007	7.059
2008	6.014
2009	5.045
2010	5.572
2011	6.464
2012	6.521
2013	6.014
2014	6.061
2015	6.553
2016	7.114
2017	6.590
2018	7.319
2019	7.882
2020	3.448
2021	6.939
2022	7.100
2023	6.025
2024	5.700
2025	6.600
2026	7.100
2027	7.200
2028	7.000
2029	7.000