| Year | Value | | 2022 | 1.061810044277 | | 2021 | 1.1220092714315 | | 2020 | 1.122475503324 | | 2019 | 1.1809717968471 | | 2018 | 1.2499661964213 | | 2017 | 1.4220317002882 | | 2016 | 1.6666051524323 | | 2015 | 1.7231474282909 | | 2014 | 1.6896948356807 | | 2013 | 1.6100569769942 | | 2012 | 1.6481757926793 | | 2011 | 1.8370255592557 | | 2010 | 1.952967042268 | | 2009 | 2.0326450430722 | | 2008 | 2.1807854853702 | | 2007 | 2.3796346750971 | | 2006 | 2.6062186026133 | | 2005 | 2.714220406576 | | 2004 | 2.877531236536 | | 2003 | 3.1772852700973 | | 2002 | 3.2784547965037 | | 2001 | 2.9855685603381 | | 2000 | 2.5512651398274 | | 1999 | 2.5697674781428 | | 1998 | 2.6593832909437 | | 1997 | 2.8414852184645 | | 1996 | 2.9748118697964 | | 1995 | 3.0820362341484 | | 1994 | 3.1539346510064 | | 1993 | 3.0977369924992 | | 1992 | 3.2155006317236 | | 1991 | 3.6117447042004 | | 1990 | 3.4676995357893 | | 1989 | 3.9680989583333 | | 1988 | 5.0608766233766 | | 1987 | 6.5287427706401 | | 1986 | 7.4981305658154 | | 1985 | 7.8569330591973 | | 1984 | 8.2652320701732 | | 1983 | 7.9586739327884 | | 1982 | 7.1889606053862 | | 1981 | 7.4169096209912 | | 1980 | 6.1603102779573 | | 1979 | 6.4689378757515 | | 1978 | 9.9407134825718 | | 1977 | 13.112058465286 | | 1976 | 13.726896112173 | | 1975 | 15.431846090872 | | 1974 | 17.274243507267 | | 1973 | 13.513513513513 | | 1972 | 13.564530289728 | | 1971 | 17.187012176085 | | 1970 | 15.987882867721 | | 1969 | 14.336053412463 | | 1968 | 11.133043821555 | | 1967 | 8.9076985086659 | | 1966 | 8.7182688306284 | | 1965 | 10.117434507678 | | 1964 | 10.328389830509 | | 1963 | 8.6646884272997 | | 1962 | 6.6754791804362 |
|