Year	U.S. dollars (Units)
1980	1150.686
1981	1356.398
1982	1316.278
1983	999.442
1984	1006.416
1985	851.139
1986	1248.386
1987	2015.875
1988	1560.368
1989	1885.285
1990	1285.664
1991	1511.937
1992	1543.242
1993	1469.214
1994	1815.739
1995	2119.375
1996	2163.399
1997	2238.263
1998	2106.752
1999	1872.791
2000	1910.357
2001	1910.299
2002	1998.363
2003	2147.735
2004	2405.294
2005	2677.739
2006	3130.790
2007	3633.714
2008	4285.984
2009	4276.689
2010	5192.593
2011	5913.282
2012	6631.809
2013	6904.355
2014	6851.093
2015	6413.903
2016	6430.416
2017	6965.195
2018	7187.688
2019	7233.468
2020	6320.089
2021	6848.211
2022	7336.241
2023	7932.905
2024	8290.943
2025	8566.977
2026	8839.338
2027	9115.392
2028	9396.777
2029	9684.880