| Year | Value | | 2022 | 1.380554439044 | | 2021 | 1.651133269596 | | 2020 | 1.4814673628535 | | 2019 | 1.4876277184246 | | 2018 | 1.7311614723006 | | 2017 | 1.6072960027936 | | 2016 | 1.5086998099132 | | 2015 | 1.352075866632 | | 2014 | 1.4092172065043 | | 2013 | 1.4483490349087 | | 2012 | 1.5105831152374 | | 2011 | 1.4873512983834 | | 2010 | 1.486897404448 | | 2009 | 1.5237851166604 | | 2008 | 1.5628735681098 | | 2007 | 1.5873821033763 | | 2006 | 1.6266729599604 | | 2005 | 1.8790685541972 | | 2004 | 2.1050164081563 | | 2003 | 2.1789585300808 | | 2002 | 2.4039798371433 | | 2001 | 2.2851817934017 | | 2000 | 2.4074646288127 | | 1999 | 2.5936425826379 | | 1998 | 1.5879082910158 | | 1997 | 1.6508393412051 | | 1996 | 1.7817985582998 | | 1995 | 1.9853144909791 | | 1994 | 2.5312465222757 | | 1993 | 3.1148431559082 | | 1992 | 3.1702630395665 | | 1991 | 3.0503691590946 | | 1990 | 3.0585616965872 | | 1989 | 3.2123053989818 | | 1988 | 3.2365292200524 | | 1987 | 3.0797473846814 | | 1986 | 3.1651807546949 | | 1985 | 2.9714808260234 | | 1984 | 3.1167025858942 | | 1983 | 3.3133802982337 | | 1982 | 3.0968133653056 | | 1981 | 3.2171055392588 | | 1980 | 3.8624663715932 | | 1979 | 4.604633986491 | | 1978 | 5.1120905501807 | | 1977 | 5.385723583457 | | 1976 | 5.1935732388368 | | 1975 | 6.253043237134 | | 1974 | 4.2168725704292 | | 1973 | 4.6734082411357 | | 1972 | 5.0198262106115 | | 1971 | 4.8084184159656 | | 1970 | 4.973806256233 | | 1969 | 6.5924779356012 | | 1968 | 5.8093847645654 | | 1967 | 4.8422014290522 | | 1966 | 3.5244153677708 | | 1965 | 3.2445928543925 | | 1964 | 2.3443435602106 | | 1963 | 2.1248828196471 | | 1962 | 2.2932670411755 | | 1961 | 2.407719002504 | | 1960 | 2.4025295429193 |
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