Year	Percent change (Units)
1981	8.998
1982	12.511
1983	18.608
1984	11.926
1985	11.054
1986	13.853
1987	35.511
1988	26.372
1989	-0.974
1990	23.200
1991	7.388
1992	36.090
1993	18.309
1994	65.965
1995	74.950
1996	6.700
1997	15.160
1998	53.146
1999	28.231
2000	35.445
2001	22.121
2002	11.480
2003	9.824
2004	13.695
2005	16.561
2006	10.138
2007	7.523
2008	9.945
2009	7.580
2010	6.270
2011	9.798
2012	34.577
2013	23.500
2014	24.152
2015	24.855
2016	19.969
2017	7.061
2018	9.892
2019	11.527
2020	7.645
2021	11.529
2022	25.430
2023	40.014
2024	18.317
2025	9.833
2026	7.604
2027	6.526
2028	6.494
2029	6.500