Year	current US$
1970	0.813303948220948
1971	0.8213536428273154
1972	0.9164844034359032
1973	0.7888705405398602
1974	0.5831949724044847
1975	1.0294209182142817
1976	1.1203669049488882
1977	1.2269525003423276
1978	1.3552566853344754
1979	1.9916994334224742
1980	2.072766666650232
1981	1.9719845958883755
1982	1.7500924419516823
1983	2.0436316707738547
1984	1.7230027682388336
1985	2.5017543156748356
1986	2.5854289930673393
1987	1.9970550191573144
1988	1.863864854936021
1989	1.7094807878006253
1990	3.0223348548867137
1991	3.7145284466905384
1992	2.923081668996361
1993	2.229832924678597
1994	1.866221284791713
1995	1.3481266094109896
1996	2.655599283695914
1997	0.32609361337212084
1998	0.3079166720417128
1999	0.3586665149217198
2000	0.5226634923455477
2001	0.6845680301868238
2002	0.7601639309110776
2003	0.993641791522712
2004	0.8416613005470656
2005	1.1608371277117182
2006	1.5547365876989165
2007	1.440431877485551
2008	1.9041879655702418
2009	2.176044586330431
2010	1.9059230176726567
2011	4.212127036454095
2012	3.401644453189819
2013	3.335079159067744
2014	4.376432975758905
2015	2.9946848853750883
2016	4.335318061824634
2017	3.654228127967762
2018	2.671444416496047
2019	1.579081613969816
2020	2.489327783167422
2021	2.6308618280293063