Year	Percent change (Units)
1980	20.627
1981	24.199
1982	18.681
1983	19.742
1984	12.578
1985	4.378
1986	23.722
1987	27.708
1988	28.900
1989	17.401
1990	9.000
1991	20.168
1992	24.476
1993	22.472
1994	34.862
1995	49.320
1996	23.918
1997	16.544
1998	18.454
1999	20.240
2000	12.292
2001	11.538
2002	15.827
2003	15.573
2004	15.324
2005	10.252
2006	12.000
2007	18.414
2008	25.304
2009	10.816
2010	12.299
2011	21.527
2012	30.570
2013	34.700
2014	15.560
2015	11.919
2016	9.050
2017	9.641
2018	30.226
2019	34.685
2020	36.430
2021	40.214
2022	45.752
2023	41.500
2024	37.500
2025	32.500
2026	27.500
2027	25.000
2028	25.000
2029	25.000