Year	Percent change (Units)
1980	25.932
1981	27.393
1982	24.860
1983	19.526
1984	16.283
1985	23.906
1986	18.848
1987	23.334
1988	28.100
1989	25.935
1990	29.115
1991	30.318
1992	27.020
1993	22.449
1994	22.851
1995	20.884
1996	20.803
1997	18.476
1998	18.650
1999	10.876
2000	9.218
2001	7.958
2002	6.350
2003	7.120
2004	5.906
2005	5.048
2006	4.303
2007	5.543
2008	7.001
2009	4.193
2010	2.268
2011	3.415
2012	3.174
2013	2.022
2014	2.905
2015	4.991
2016	7.507
2017	4.312
2018	3.241
2019	3.524
2020	2.525
2021	3.505
2022	10.183
2023	11.729
2024	6.390
2025	3.597
2026	3.044
2027	2.956
2028	3.003
2029	2.999