Year	current US$
2003	6.15071518
2004	6.87111947
2005	8.35642958
2006	6.03279124
2007	5.49363229
2008	4.98525276
2009	4.41090902
2010	6.06346519
2011	6.37929299
2012	6.76818653
2013	7.14559362
2014	7.34282555
2015	7.4638439
2016	7.34956662
2017	7.23917843
2018	8.01840003
2019	8.30965978
2020	8.07924646
2021	7.95265803