Year	Percent change (Units)
1980	11.729
1981	13.997
1982	12.495
1983	19.692
1984	20.019
1985	37.430
1986	47.986
1987	43.035
1988	45.818
1989	113.161
1990	93.873
1991	85.280
1992	146.714
1993	158.403
1994	46.073
1995	31.456
1996	38.581
1997	21.418
1998	22.664
1999	23.861
2000	24.091
2001	21.357
2002	22.239
2003	21.400
2004	17.969
2005	18.325
2006	9.017
2007	10.655
2008	12.449
2009	13.392
2010	8.500
2011	8.658
2012	6.575
2013	6.978
2014	7.811
2015	10.107
2016	17.870
2017	6.577
2018	7.495
2019	9.151
2020	15.733
2021	22.021
2022	10.993
2023	10.953
2024	11.370
2025	7.815
2026	7.000
2027	7.000
2028	7.000
2029	7.000