Year	U.S. dollars (Units)
1980	2146.470
1981	2371.712
1982	2559.063
1983	2567.340
1984	2619.583
1985	2710.017
1986	2755.167
1987	2708.269
1988	2292.215
1989	2250.821
1990	2397.225
1991	2580.386
1992	2871.870
1993	3071.246
1994	3207.884
1995	3212.815
1996	3711.349
1997	3929.349
1998	4173.999
1999	4286.698
2000	4261.463
2001	4244.106
2002	4324.661
2003	4469.688
2004	4807.660
2005	5146.047
2006	5598.289
2007	6350.183
2008	7369.186
2009	7806.732
2010	8332.576
2011	9653.933
2012	11063.257
2013	12273.180
2014	13221.567
2015	14102.156
2016	14866.506
2017	15731.102
2018	16181.217
2019	16526.419
2020	13342.722
2021	15540.795
2022	17409.626
2023	18725.739
2024	19369.476
2025	20092.016
2026	21058.012
2027	22070.452
2028	23131.568
2029	24243.702