Year	Percent change (Units)
1981	27.414
1982	98.900
1983	80.701
1984	59.184
1985	63.739
1986	105.755
1987	159.174
1988	51.657
1989	19.697
1990	29.930
1991	18.795
1992	11.938
1993	8.009
1994	7.051
1995	51.966
1996	27.704
1997	15.719
1998	18.609
1999	12.319
2000	8.959
2001	4.403
2002	5.700
2003	3.977
2004	5.191
2005	3.333
2006	4.053
2007	3.759
2008	6.528
2009	3.574
2010	4.402
2011	3.819
2012	3.568
2013	3.974
2014	4.081
2015	2.131
2016	3.360
2017	6.773
2018	4.831
2019	2.829
2020	3.150
2021	7.355
2022	7.817
2023	4.420
2024	3.515
2025	3.014
2026	3.002
2027	3.001
2028	3.000
2029	3.000