| Year | Value | | 2022 | 5.4419226231871 | | 2021 | 3.1115370601969 | | 2020 | 2.8389859874966 | | 2019 | 3.1462170772213 | | 2018 | 1.9633324310002 | | 2017 | 1.8745422881596 | | 2016 | 1.8403823872401 | | 2015 | 1.6744228949456 | | 2014 | 1.8182888625159 | | 2013 | 1.6762053611586 | | 2012 | 1.6246431175672 | | 2011 | 1.526063748465 | | 2010 | 1.6588579881308 | | 2009 | 1.6380125632141 | | 2008 | 1.7221862435576 | | 2005 | 1.4574402023059 | | 2004 | 1.4060480961251 | | 2003 | 1.3656998389526 | | 1995 | 1.8575256340078 | | 1994 | 2.5843108504399 | | 1993 | 4.0306556911723 | | 1992 | 2.9312288613303 | | 1991 | 2.8593508500773 | | 1990 | 3.1224858757062 | | 1989 | 3.0940685820204 | | 1988 | 3.1249086924763 | | 1987 | 3.5034908700322 | | 1986 | 2.845058855735 | | 1985 | 2.5079834417504 | | 1984 | 2.185149776928 | | 1983 | 2.0969798657718 | | 1982 | 2.2591768631813 | | 1981 | 2.372480620155 | | 1980 | 2.1946308724832 | | 1979 | 2.2490601503759 | | 1978 | 2.7142857142857 | | 1977 | 3.0722748815166 | | 1976 | 2.4952311078503 | | 1975 | 1.8565861262666 | | 1974 | 1.4919546213084 | | 1973 | 1.6949152542373 | | 1972 | 1.4756438809891 | | 1971 | 1.4083129584352 | | 1970 | 1.3683953564066 | | 1969 | 1.2822353684452 | | 1968 | 1.3588634959852 | | 1967 | 1.3397397678252 | | 1966 | 1.3374776302157 | | 1965 | 1.8953857478033 | | 1964 | 2.1571127475215 | | 1963 | 0.83995528295616 | | 1962 | 0.546875 | | 1961 | 0.26556291390728 |
|