Year Measure 1971 0.00166 1972 0.00161 1973 0.00226 1974 0.00301 1975 0.00336 1976 0.00324 1977 0.00387 1978 0.00469 1979 0.00664 1980 0.00432 1981 0.00372 1982 0.00357 1983 0.00349 1984 0.00347 1985 0.00339 1986 0.00326 1987 0.01383 1988 0.01353 1989 0.01321 1990 0.01287 1991 0.00433 1992 0.00327 1993 0.00271 1994 0.00245 1995 0.00242 1996 0.00234 1997 0.0023 1998 0.00228 1999 0.00225 2000 0.0022 2001 0.00216 2002 0.00176 2003 0.00144 2004 0.00159 2005 0.01886 2006 0.01863 2007 0.01703 2008 0.01005 2009 0.00903 2010 0.01294