| Year | Value | | 2021 | 0.0070068082820474 | | 2020 | 0.0054283302806272 | | 2019 | 0.019746376205282 | | 2018 | 0.022232686951514 | | 2017 | 0.023396208340472 | | 2016 | 0.021929058525358 | | 2015 | 0.023530057687858 | | 2014 | 0.02329710232248 | | 2013 | 0.007732708747525 | | 2012 | 0.026773022142989 | | 2011 | 0.0037856519338001 | | 2010 | 0.024656464673907 | | 2009 | 0.02419755180646 | | 2008 | 0.024861550813361 | | 2007 | 0.022818929466223 | | 2006 | 0.060871565789221 | | 2005 | 0.0185411893792 | | 2004 | 0.002912665062053 | | 2003 | 0.0013863741602039 | | 2002 | 0.0013953657113993 | | 2001 | 0.00194689970129 | | 2000 | 0.0054934252373738 | | 1999 | 0.0072489156830291 | | 1998 | 0.012206874397687 | | 1997 | 0.014296868985692 | | 1996 | 0.0039171905909082 | | 1995 | 0.0088564620542775 | | 1994 | 0.01354096140826 | | 1991 | 0.020963184514407 | | 1990 | 0.023094367137102 | | 1989 | 0.016577954393643 | | 1988 | 0.038250231988515 | | 1987 | 0.052612096480009 | | 1986 | 0.066634935744883 | | 1985 | 0.061431350465854 | | 1984 | 0.066115702479339 | | 1983 | 0.060262745570688 | | 1982 | 0.066365808335546 | | 1981 | 0.077172403148634 | | 1980 | 0.10495014867938 | | 1979 | 0.060988005692214 | | 1978 | 0.07185628742515 | | 1977 | 0.081721601743394 | | 1976 | 0.059364796675571 | | 1975 | 0.072939460247994 | | 1974 | 0.15432098765432 | | 1973 | 0.47596382674917 | | 1972 | 0.57381324986959 |
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