Year % of output 1971 7.398568019093078 1972 7.422068283028203 1973 9.967992684042066 1974 8.453788874288218 1975 13.275968039336203 1976 11.260997067448681 1977 9.383995394358088 1978 11.154489682097044 1979 13.49911190053286 1980 14.677804295942721 1981 15.736342042755345 1982 12.791878172588833 1983 14.47435246317928 1984 16.778115501519757 1985 17.114914425427873 1986 16.840882694541232 1987 17.681940700808628 1988 19.8798470780994 1989 22.739877981142538 1990 14.564686737184704 1991 18.040508714083845 1992 10.977744436109028 1993 0 1994 10.848167539267015 1995 10.842340024017842 1996 10.814839350778403 1997 10.807354116706634 1998 9.907407407407408 1999 9.819942502647905 2000 8.522555252800485 2001 8.473557692307693 2002 8.91260455725411 2003 8.67618247970893 2004 10.128862408202854 2005 11.506332524925895 2006 12.578616352201259 2007 11.040693795863909 2008 23.778040141676506 2009 22.305593451568896 2010 20.87962962962963 2011 22.01099404489235 2012 25.94173782019086 2013 27.473077886301027 2014 26.7458777885548