Year	U.S. dollars (Units)
1980	5948.312
1981	5422.695
1982	5623.925
1983	5050.595
1984	4895.517
1985	4832.492
1986	5670.974
1987	6577.878
1988	7632.639
1989	7879.212
1990	9679.318
1991	10282.862
1992	11234.158
1993	10451.746
1994	11122.873
1995	12997.468
1996	13776.645
1997	13484.158
1998	13526.648
1999	13901.641
2000	12268.279
2001	12579.395
2002	14185.446
2003	18534.603
2004	22015.177
2005	22608.424
2006	24858.548
2007	28899.982
2008	32173.559
2009	29829.328
2010	26743.400
2011	25437.036
2012	21844.999
2013	21712.064
2014	21554.224
2015	18023.859
2016	17906.100
2017	18552.223
2018	19750.710
2019	19140.612
2020	17570.395
2021	20115.924
2022	20818.073
2023	22805.197
2024	23965.779
2025	24952.668
2026	25909.598
2027	26783.275
2028	27693.171
2029	28628.224