| Year | Value | | 2022 | 2.4767786677464 | | 2021 | 2.6367002616005 | | 2020 | 2.7097783729293 | | 2019 | 2.3832777774615 | | 2018 | 1.9764487201196 | | 2017 | 2.0318293262215 | | 2016 | 2.224984729702 | | 2015 | 2.1395916294647 | | 2014 | 1.8068874807375 | | 2013 | 1.5597373837127 | | 2012 | 1.4398739449801 | | 2011 | 1.4862578010289 | | 2010 | 1.2361705205762 | | 2009 | 1.2949496088007 | | 2008 | 1.2906249257454 | | 2007 | 1.2609938563665 | | 2006 | 1.4463624243599 | | 2005 | 1.4516014162103 | | 2004 | 1.4259020629651 | | 2003 | 1.4838857036399 | | 2002 | 1.4926429262434 | | 2001 | 1.5211124733646 | | 2000 | 1.5479040325129 | | 1999 | 1.5560757573087 | | 1998 | 1.6779715154667 | | 1997 | 1.7263845443223 | | 1996 | 1.867535229032 | | 1995 | 1.744707585825 | | 1994 | 1.7421232116496 | | 1993 | 1.7321139551023 | | 1992 | 1.7061258775943 | | 1991 | 1.8337085277651 | | 1990 | 1.8394565888668 | | 1989 | 2.1145503906304 | | 1988 | 2.1034758517182 | | 1987 | 1.823184593083 | | 1986 | 2.086676102882 | | 1985 | 2.3355734273438 | | 1984 | 2.7553414597424 | | 1983 | 4.1672583490453 | | 1982 | 3.6919035688117 | | 1981 | 2.481077792701 | | 1980 | 2.0287193436513 | | 1979 | 2.2381930184805 | | 1978 | 2.4880228672652 | | 1977 | 2.3814955061818 | | 1976 | 1.862390067253 | | 1975 | 1.7399793269783 | | 1974 | 1.3115389585218 | | 1973 | 1.3984191783202 | | 1972 | 1.4145199063232 | | 1971 | 1.4752610077168 | | 1970 | 1.5616728427739 | | 1969 | 1.3142350856468 | | 1968 | 1.4426846479536 | | 1967 | 1.421052631579 | | 1966 | 1.3174748398902 | | 1965 | 1.2877186238708 | | 1964 | 1.7441860465116 | | 1963 | 1.5080113100848 | | 1962 | 1.7296050735082 | | 1961 | 2.2159090909091 | | 1960 | 2.0047875523639 |
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