Year	Percent change (Units)
1980	28.699
1981	4.787
1982	7.003
1983	16.657
1984	31.158
1985	23.114
1986	10.722
1987	8.364
1988	8.554
1989	17.177
1990	29.809
1991	80.193
1992	40.194
1993	30.124
1994	26.795
1995	25.567
1996	15.829
1997	9.167
1998	7.851
1999	6.782
2000	5.956
2001	8.546
2002	7.225
2003	13.836
2004	13.709
2005	12.561
2006	5.655
2007	16.819
2008	16.844
2009	10.215
2010	11.744
2011	6.008
2012	8.002
2013	9.473
2014	6.357
2015	3.661
2016	1.725
2017	5.235
2018	2.440
2019	6.219
2020	5.180
2021	7.321
2022	9.361
2023	6.900
2024	5.500
2025	5.000
2026	5.040
2027	5.000
2028	5.000
2029	5.000