Year	constant 2015 US$
1998	18759.166845194377
1999	18442.688812332417
2000	19343.140807028936
2001	19963.51743955726
2002	19428.172193071634
2003	18965.954567703255
2004	19023.51342454941
2005	18885.474051392608
2006	19709.038215312758
2007	20182.642631306026
2008	20767.576460400913
2009	21502.4762195871
2010	20295.283542090143
2011	18868.13860883664
2012	18638.180326638823
2013	18544.502671354123
2014	17693.646946917786
2015	18237.643050184524
2016	18313.37934932835
2017	17600.454267867055
2018	17231.235853463222
2019	16830.722958115683
2020	16491.291631342054
2021	17080.97827507707