Year	Percent change (Units)
1980	28.697
1981	21.353
1982	7.190
1983	3.421
1984	2.274
1985	2.460
1986	2.750
1987	3.048
1988	7.147
1989	5.700
1990	8.574
1991	9.333
1992	6.213
1993	4.801
1994	6.266
1995	4.481
1996	4.925
1997	4.439
1998	7.514
1999	0.813
2000	2.259
2001	4.067
2002	2.762
2003	3.515
2004	3.591
2005	2.754
2006	2.242
2007	2.535
2008	4.674
2009	2.756
2010	2.939
2011	4.026
2012	2.187
2013	1.301
2014	1.275
2015	0.706
2016	0.972
2017	1.944
2018	1.476
2019	0.383
2020	0.537
2021	2.498
2022	5.090
2023	3.593
2024	2.522
2025	2.000
2026	2.000
2027	2.000
2028	2.000
2029	2.000