| Year | Value | | 2022 | 4.350272042691 | | 2021 | 3.690919588022 | | 2020 | 3.2902906279833 | | 2019 | 3.4642805799902 | | 2018 | 3.4944584885618 | | 2017 | 5.3187160522893 | | 2016 | 5.1747662930149 | | 2015 | 5.588169529593 | | 2014 | 6.1316143298801 | | 2013 | 7.8707236457396 | | 2012 | 16.001093850634 | | 2011 | 12.690969469916 | | 2010 | 6.200155956474 | | 2009 | 12.142227874299 | | 2008 | 10.278393762114 | | 2007 | 7.0255143697477 | | 2006 | 7.2509726208255 | | 2005 | 5.0345700926716 | | 2004 | 4.7358014394906 | | 2003 | 5.3035662150978 | | 2002 | 5.317833661182 | | 2001 | 5.1474680022262 | | 2000 | 5.9239610963748 | | 1999 | 7.8904333605888 | | 1998 | 12.799754047961 | | 1997 | 16.09065492832 | | 1996 | 20.977259643063 | | 1995 | 27.427785419532 | | 1994 | 34.083364072298 | | 1993 | 25.277264325323 | | 1992 | 21.846846846847 | | 1991 | 28.695652173913 | | 1990 | 35.826771653543 | | 1989 | 25.849838261166 | | 1988 | 31.186718284693 | | 1987 | 29.949369537876 | | 1986 | 32.432201580184 | | 1985 | 33.282103825137 | | 1984 | 36.145941505603 | | 1983 | 27.055927530524 | | 1982 | 28.932334645169 | | 1981 | 25.650023927261 | | 1980 | 30.197300103842 | | 1979 | 12.948627726953 | | 1978 | 6.5750000000001 | | 1977 | 11.604138103012 | | 1976 | 6.8593500265325 | | 1975 | 26.057756884157 | | 1974 | 19.598393574215 | | 1973 | 10.396807803217 | | 1972 | 7.6354092100104 | | 1971 | 4.7750000000238 | | 1970 | 3.4928848641836 | | 1969 | 16.41566265 | | 1968 | 15.598885795483 | | 1967 | 12.187499998437 | | 1966 | 9.777015439276 |
|