Year	Percent change (Units)
1981	11.483
1982	0.400
1983	7.000
1984	3.200
1985	0.100
1986	13.900
1987	25.000
1988	41.200
1989	44.800
1990	40.400
1991	52.687
1992	27.335
1993	32.698
1994	75.409
1995	36.901
1996	51.716
1997	80.473
1998	20.846
1999	9.600
2000	9.600
2001	9.422
2002	9.031
2003	9.976
2004	15.244
2005	17.195
2006	24.562
2007	27.559
2008	24.834
2009	16.087
2010	12.890
2011	11.939
2012	10.406
2013	7.134
2014	6.426
2015	4.183
2016	5.123
2017	7.690
2018	9.045
2019	7.674
2020	9.353
2021	9.490
2022	25.181
2023	17.142
2024	10.900
2025	5.430
2026	5.008
2027	4.998
2028	5.029
2029	5.039