| Year | Value | | 2022 | 1.226636566126 | | 2021 | 1.9890768559212 | | 2020 | 2.1273628177791 | | 2019 | 2.2575097536502 | | 2018 | 2.3651026578667 | | 2017 | 2.4850093419051 | | 2016 | 4.8358501350833 | | 2015 | 9.2199178876905 | | 2014 | 11.794015655954 | | 2013 | 6.4819286415685 | | 2012 | 1.4227878171389 | | 2011 | 2.5458104562831 | | 2010 | 2.1991513135755 | | 2009 | 2.2011769503756 | | 2008 | 2.4327765640263 | | 2007 | 6.3438087109433 | | 2006 | 6.7579090091297 | | 2005 | 2.6067225740821 | | 2004 | 2.4946254249127 | | 2003 | 2.260009348102 | | 2002 | 2.1501680651457 | | 2001 | 2.0967775896561 | | 2000 | 2.106594082731 | | 1999 | 2.1720112045738 | | 1998 | 2.312427402948 | | 1997 | 2.6759129883941 | | 1996 | 3.3196638427685 | | 1995 | 4.1219562508752 | | 1994 | 4.8467426068714 | | 1993 | 5.2607196438357 | | 1992 | 5.3245264072287 | | 1991 | 5.2003568784346 | | 1990 | 4.9964592337802 | | 1989 | 4.7558091495383 | | 1988 | 4.6179941398436 | | 1987 | 4.5777832445483 | | 1986 | 4.5577190037184 | | 1985 | 4.5182658004112 | | 1984 | 4.4773339184401 | | 1983 | 4.4076651755183 | | 1982 | 4.2312237919546 | | 1981 | 3.9687246287343 | | 1980 | 3.6203882226384 | | 1979 | 3.2791631302459 | | 1978 | 3.1263145496185 | | 1977 | 3.0518049816697 | | 1976 | 3.0539119018226 | | 1975 | 3.1800472980167 | | 1974 | 3.3477414707115 | | 1973 | 3.6077285065359 | | 1972 | 4.0990358169709 | | 1971 | 4.944874854499 | | 1970 | 6.0171557788717 | | 1969 | 7.0471412203099 | | 1968 | 7.6748572380089 | | 1967 | 7.6241055144594 | | 1966 | 7.0008688025349 | | 1965 | 6.0338019129832 | | 1964 | 5.0646911935771 | | 1963 | 4.5995452120823 | | 1962 | 4.6838965312215 | | 1961 | 5.0490553226567 |
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