Year	constant 2015 US$
1973	390000
1974	16000000
1975	29420000
1976	16300000
1977	17320000
1978	22120000
1979	23360000
1980	38740000
1981	34070000
1982	38160000
1983	23590000
1984	36560000
1985	39790000
1986	23700000
1987	27100000
1988	28490000
1989	37150000
1990	26910000
1991	23710000
1992	15940000
1993	12230000
1994	24100000
1995	26220000
1996	50110000
1997	16840000
1998	24680000
1999	11230000
2000	18870000
2001	26890000
2002	37350000
2003	12610000
2004	30600000
2005	22280000
2006	19850000
2007	17760000
2008	18160000
2009	31730000
2010	28870000
2011	20120000
2012	22770000
2013	17230000
2014	14020000
2015	11660000
2016	8570000
2017	18260000