Year	Percent change (Units)
1981	10.900
1982	11.349
1983	14.414
1984	1.565
1985	6.899
1986	21.696
1987	9.140
1988	8.967
1989	10.229
1990	5.561
1991	15.136
1992	19.300
1993	5.861
1994	9.082
1995	8.697
1996	5.993
1997	5.673
1998	12.011
1999	9.017
2000	0.596
2001	3.407
2002	3.510
2003	6.090
2004	2.022
2005	6.650
2006	8.273
2007	4.732
2008	10.695
2009	11.087
2010	9.026
2011	9.582
2012	11.475
2013	7.749
2014	8.084
2015	7.576
2016	10.439
2017	2.711
2018	4.580
2019	6.021
2020	4.776
2021	4.187
2022	8.081
2023	7.437
2024	5.727
2025	5.500
2026	5.400
2027	5.400
2028	5.400
2029	5.400