Year	U.S. dollars (Units)
1980	4549.590
1981	4352.502
1982	4452.666
1983	4399.223
1984	4575.652
1985	4824.674
1986	6057.903
1987	7188.216
1988	8204.300
1989	8635.765
1990	10359.998
1991	10413.726
1992	12158.597
1993	11342.407
1994	12525.318
1995	15396.919
1996	15260.553
1997	14324.090
1998	15181.803
1999	15379.994
2000	14464.952
2001	14905.024
2002	16188.531
2003	20389.337
2004	23969.991
2005	25527.252
2006	27448.569
2007	31774.426
2008	36009.560
2009	32650.090
2010	31521.893
2011	32910.616
2012	29075.120
2013	27671.485
2014	27076.651
2015	23507.588
2016	24802.469
2017	26834.797
2018	29631.854
2019	29626.370
2020	28386.270
2021	32926.615
2022	32357.237
2023	34956.733
2024	37148.586
2025	38664.883
2026	40356.372
2027	42157.386
2028	43961.910
2029	45757.884