Year	constant 2015 US$
1997	317.107801465161
1998	327.26071929621344
1999	314.8750710642604
2000	314.7572703332365
2001	304.59953859188147
2002	308.62444696021817
2003	293.70451837639797
2004	294.5773026654735
2005	290.04006187240464
2006	297.6694681717082
2007	297.62280020319776
2008	300.02121478776155
2009	293.988898670574
2010	296.15348891448417
2011	296.6704479898629
2012	300.6293895577122
2013	305.51065183648035
2014	306.8986514274932
2015	289.3928463060642
2016	282.8168359205021
2017	278.1263329848028
2018	274.7886646468227
2019	271.03561727812956
2020	265.08939555552024
2021	265.2776288199803
2022	263.50973732134725
2023	262.86225222864965