Year	U.S. dollars (Units)
1980	144.492
1981	165.128
1982	163.054
1983	174.291
1984	180.152
1985	182.892
1986	194.619
1987	197.599
1988	228.087
1989	225.476
1990	226.445
1991	241.458
1992	213.342
1993	223.029
1994	227.325
1995	241.150
1996	243.348
1997	259.233
1998	252.809
1999	255.294
2000	266.158
2001	269.250
2002	269.082
2003	281.039
2004	319.068
2005	354.973
2006	388.995
2007	440.856
2008	532.331
2009	542.536
2010	671.998
2011	795.314
2012	794.093
2013	809.346
2014	827.394
2015	882.308
2016	880.225
2017	1027.965
2018	1161.534
2019	1185.682
2020	1139.192
2021	1229.470
2022	1336.547
2023	1319.643
2024	1397.080
2025	1519.955
2026	1647.083
2027	1785.318
2028	1937.214
2029	2102.012