Year	U.S. dollars (Units)
1980	5703.963
1981	5995.182
1982	6139.013
1983	5590.161
1984	6170.503
1985	6490.372
1986	7380.118
1987	9015.195
1988	10527.458
1989	12012.634
1990	13374.312
1991	15297.577
1992	17710.506
1993	20065.680
1994	22194.005
1995	23070.541
1996	24698.956
1997	27214.595
1998	25649.085
1999	24969.005
2000	25574.491
2001	25166.902
2002	24731.081
2003	23856.482
2004	24873.898
2005	26551.769
2006	28028.157
2007	30494.551
2008	31487.940
2009	30593.991
2010	32421.361
2011	34955.147
2012	36623.745
2013	38233.352
2014	40185.303
2015	42325.352
2016	43488.204
2017	46025.665
2018	48310.038
2019	48277.982
2020	46446.056
2021	49848.567
2022	48001.536
2023	50029.777
2024	53606.486
2025	56049.859
2026	58524.952
2027	61081.293
2028	63741.272
2029	66488.289