Year | Value | 2022 | 2.2805558496654 | 2021 | 2.3164882528028 | 2020 | 2.332086250689 | 2019 | 2.355238072353 | 2018 | 2.3941846253096 | 2017 | 2.3910852337636 | 2016 | 2.3888657546752 | 2015 | 2.3884050787152 | 2014 | 2.3902882079708 | 2013 | 2.4066796920457 | 2012 | 2.7760077757071 | 2011 | 3.2441412452308 | 2010 | 4.1558972223647 | 2009 | 4.0171059238912 | 2008 | 3.3131079690881 | 2007 | 3.6815587625746 | 2006 | 3.7536054991551 | 2005 | 3.5987719660308 | 2004 | 3.3977060124824 | 2003 | 2.7680161423113 | 2002 | 2.3403944253138 | 2001 | 3.7596330717317 | 2000 | 3.816978871538 | 1999 | 2.6704756725991 | 1998 | 2.1379627146322 | 1997 | 2.0536835141427 | 1996 | 2.6728442333293 | 1995 | 2.7013971355994 | 1994 | 2.8520446261962 | 1993 | 2.8626860627574 | 1992 | 2.745972234036 | 1991 | 2.779776802472 | 1990 | 2.8169116283088 | 1989 | 2.8800596545285 | 1988 | 2.9125041813054 | 1987 | 2.9579413295134 | 1986 | 2.9761824172011 | 1985 | 2.9929202774016 | 1984 | 2.5238149653545 | 1983 | 2.0819779398831 | 1982 | 2.17312144775 | 1981 | 2.2317832424501 | 1980 | 2.268973355286 | 1979 | 2.3201080285884 | 1978 | 2.3760973397688 | 1977 | 2.4181396597576 | 1976 | 2.4608327993737 | 1975 | 2.7865768453687 | 1974 | 3.0982937059334 | 1973 | 3.1019842449689 | 1972 | 3.0845742859865 | 1971 | 3.0434317931028 | 1970 | 3.0002017751461 | 1969 | 2.9621576257799 | 1968 | 2.9155154603309 | 1967 | 2.8724080719947 | 1966 | 2.833715085348 | 1965 | 2.7833399707246 | 1964 | 2.7339459026609 | 1963 | 2.6833270798071 | 1962 | 2.6340239054077 | 1961 | 2.593543413614 |
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