Year	Percent change (Units)
1980	55.701
1981	49.290
1982	59.866
1983	76.645
1984	18.816
1985	35.936
1986	13.507
1987	24.440
1988	20.607
1989	25.281
1990	7.229
1991	7.520
1992	1.519
1993	4.749
1994	0.515
1995	1.999
1996	2.057
1997	2.048
1998	1.275
1999	5.529
2000	4.148
2001	8.650
2002	1.955
2003	2.763
2004	3.916
2005	4.135
2006	6.965
2007	5.865
2008	18.113
2009	7.464
2010	2.526
2011	5.235
2012	4.243
2013	4.140
2014	0.809
2015	2.005
2016	1.900
2017	1.865
2018	3.725
2019	2.009
2020	3.580
2021	5.127
2022	9.589
2023	7.750
2024	4.800
2025	2.763
2026	2.500
2027	2.500
2028	2.500
2029	2.500