Year	U.S. dollars (Units)
1980	3338.764
1981	3296.654
1982	3095.096
1983	2838.655
1984	2596.075
1985	2716.645
1986	3774.582
1987	4724.451
1988	5532.620
1989	5977.577
1990	7957.244
1991	9026.301
1992	10863.487
1993	9547.643
1994	9977.615
1995	11787.315
1996	12187.582
1997	11594.755
1998	12216.689
1999	12487.712
2000	11531.467
2001	11734.878
2002	12927.584
2003	15793.852
2004	18055.893
2005	18790.561
2006	19840.474
2007	22813.667
2008	24946.256
2009	23126.175
2010	22539.038
2011	23213.126
2012	20576.825
2013	21653.505
2014	22109.318
2015	19252.015
2016	19986.362
2017	21482.834
2018	23573.299
2019	23333.317
2020	22224.566
2021	24838.734
2022	24798.524
2023	27880.066
2024	28969.288
2025	29982.563
2026	31234.692
2027	32506.273
2028	33829.599
2029	35153.429