Year	U.S. dollars (Units)
1980	333.918
1981	342.812
1982	365.498
1983	389.999
1984	452.288
1985	443.046
1986	470.142
1987	484.746
1988	501.620
1989	498.479
1990	564.868
1991	611.088
1992	651.332
1993	689.023
1994	787.255
1995	829.220
1996	903.331
1997	1003.944
1998	1026.150
1999	1025.700
2000	1065.469
2001	1017.154
2002	1061.683
2003	1162.710
2004	1259.771
2005	1477.595
2006	1698.156
2007	1928.714
2008	2410.801
2009	2472.242
2010	2894.260
2011	3320.074
2012	3446.355
2013	3737.366
2014	3969.713
2015	4057.742
2016	4150.367
2017	4401.055
2018	4360.149
2019	4082.694
2020	3852.390
2021	3996.572
2022	3341.996