Year Measure 1971 0.00153 1972 0.00171 1973 0.00176 1974 0.00169 1975 0.00165 1976 0.00182 1977 0.002 1978 0.00201 1979 0.00206 1980 0.00208 1981 0.00221 1982 0.00233 1983 0.00245 1984 0.00245 1985 0.00239 1986 0.00244 1987 0.00235 1988 0.00211 1989 0.00276 1990 0.00261 1991 0.00267 1992 0.00323 1993 0.00358 1994 0.00334 1995 0.00331 1996 0.00332 1997 0.00334 1998 0.00186 1999 0.00201 2000 0.00362 2001 0.00346 2002 0.00398 2003 0.00389 2004 0.00449 2005 0.00556 2006 0.00613 2007 0.00663 2008 0.00741 2009 0.00949 2010 0.00915