Year % of output 1971 7.121185079421738 1972 6.962663975782038 1973 7.256063169768754 1974 8.19500523403619 1975 8.450953497632849 1976 8.745373076173777 1977 9.580518406176754 1978 9.886610748679715 1979 9.472801536422407 1980 10.575843909177243 1981 12.00108148298354 1982 11.263193264023402 1983 11.260893009340592 1984 12.899895993806549 1985 14.551645527345594 1986 11.50028506858819 1987 11.897919520820722 1988 12.280637967810742 1989 11.954939560787292 1990 11.872311059833299 1991 11.954749022754925 1992 10.711295460450971 1993 12.317478349855515 1994 13.39488504436958 1995 13.228628905208561 1996 12.255867170453941 1997 13.020020080823528 1998 12.795553117965525 1999 13.920366040550194 2000 15.659235267761707 2001 15.25631098459902 2002 14.54492961340864 2003 14.040625857809498 2004 14.359313949704513 2005 16.053075231273482 2006 16.2545186986148 2007 17.458889520962046 2008 18.442747873889708 2009 18.229196219323267 2010 16.40718998948795 2011 16.033107247332335 2012 18.199190897073997 2013 18.517144817610298 2014 19.34338625711862