| Year | Value | | 2022 | 1.1535671778435 | | 2021 | 1.1806797235283 | | 2020 | 1.3148655415575 | | 2019 | 1.2058914622879 | | 2018 | 1.1897911701167 | | 2017 | 1.2652396703256 | | 2016 | 1.3219083994296 | | 2015 | 1.7450805494301 | | 2014 | 1.6024876224024 | | 2013 | 1.6430690510479 | | 2012 | 1.4835127927745 | | 2011 | 1.371183055287 | | 2010 | 1.4769720387309 | | 2009 | 1.5296257242254 | | 2008 | 1.2466948819293 | | 2007 | 1.3039382537083 | | 2006 | 1.4562149262596 | | 2005 | 1.5812726856548 | | 2004 | 1.3822235355104 | | 2003 | 1.5094994978724 | | 2002 | 1.5418402208765 | | 2001 | 1.7520201296484 | | 2000 | 1.7889668486954 | | 1999 | 1.9306307187099 | | 1998 | 2.0166613419493 | | 1997 | 1.9967699683355 | | 1996 | 2.5020265977258 | | 1995 | 2.6353240993563 | | 1994 | 2.4741979398929 | | 1993 | 2.7461024691822 | | 1992 | 2.5070350473267 | | 1991 | 2.0198159306892 | | 1990 | 2.6823787923049 | | 1989 | 2.1904761904762 | | 1988 | 2.1852009625016 | | 1987 | 3.4114960454495 | | 1986 | 3.3492955407313 | | 1985 | 3.8701490959078 | | 1984 | 3.3575581395349 | | 1983 | 4.8459563543004 | | 1982 | 5.1126516464471 | | 1981 | 3.9848197343454 | | 1980 | 4.5590682196339 | | 1979 | 3.352435530086 | | 1978 | 6.1997019374069 | | 1977 | 8.2143869930995 | | 1976 | 5.6769130150425 | | 1975 | 5.2162849872773 | | 1974 | 3.9329608938547 | | 1973 | 3.9253897550111 | | 1972 | 3.6308109942314 | | 1971 | 3.6195158850227 | | 1970 | 3.5064395513087 | | 1969 | 2.3875598086124 | | 1968 | 2.3573735199139 | | 1967 | 4.7036328871893 | | 1966 | 2.843567251462 | | 1965 | 3.0983463881636 | | 1964 | 3.3402275077559 | | 1963 | 3.3163913595934 | | 1962 | 2.425068119891 | | 1961 | 2.6447574334898 | | 1960 | 2.5080012727171 |
|