Year	Percent change (Units)
1980	58.548
1981	50.864
1982	51.019
1983	84.275
1984	29.170
1985	32.376
1986	21.273
1987	18.763
1988	25.456
1989	14.503
1990	15.513
1991	6.809
1992	3.959
1993	4.083
1994	1.550
1995	1.655
1996	2.252
1997	1.796
1998	1.703
1999	3.220
2000	5.120
2001	6.396
2002	5.177
2003	2.062
2004	3.152
2005	4.000
2006	6.674
2007	5.066
2008	12.680
2009	12.006
2010	5.394
2011	3.990
2012	5.195
2013	3.885
2014	2.035
2015	1.631
2016	1.693
2017	1.768
2018	2.677
2019	3.006
2020	2.848
2021	4.458
2022	8.307
2023	8.740
2024	5.609
2025	3.430
2026	2.535
2027	2.500
2028	2.500
2029	2.500