Year	constant 2015 US$
1973	520000
1974	16970000
1975	23310000
1976	17000000
1977	13730000
1978	14020000
1979	14650000
1980	21330000
1981	20630000
1982	17650000
1983	12570000
1984	9460000
1985	12940000
1986	24670000
1987	23250000
1988	26520000
1989	23110000
1990	21680000
1991	21530000
1992	23360000
1993	17900000
1994	14660000
1995	53390000
1996	30070000
1997	6220000
1998	26310000
1999	19770000
2000	7500000
2001	11840000
2002	6030000
2003	7160000
2004	10490000
2005	8070000
2006	4850000
2007	60050000
2008	23150000
2009	25810000
2010	15260000
2011	14910000
2012	7330000
2013	7510000
2014	8680000
2015	13920000
2016	9120000
2017	7200000