| Year | Value | | 2022 | 1.4159704216438 | | 2021 | 1.3773468250001 | | 2020 | 1.2124665328638 | | 2019 | 1.029548733859 | | 2018 | 1.0450986872163 | | 2017 | 1.0761188600928 | | 2016 | 1.0852890443715 | | 2015 | 1.0858484651446 | | 2014 | 1.1029104242038 | | 2013 | 1.1054126162636 | | 2012 | 1.1074711981864 | | 2011 | 1.1246627597711 | | 2010 | 1.1094177050799 | | 2009 | 1.0945118511787 | | 2008 | 1.1422780333843 | | 2007 | 1.206525000682 | | 2006 | 1.230576923254 | | 2005 | 1.2423234271762 | | 2004 | 1.2749619889747 | | 2003 | 1.3008692060697 | | 2002 | 1.3427039041408 | | 2001 | 1.4010606816815 | | 2000 | 1.4619149984973 | | 1999 | 1.5279741476591 | | 1998 | 1.5604514994735 | | 1997 | 1.4976484972917 | | 1996 | 1.2958727048787 | | 1995 | 1.1918148147554 | | 1994 | 1.2659756258677 | | 1993 | 1.3197689951663 | | 1992 | 1.2586651971685 | | 1991 | 1.3465499934412 | | 1990 | 1.5454405131459 | | 1989 | 1.6230429455409 | | 1988 | 1.7673132191978 | | 1987 | 1.9325456182495 | | 1986 | 2.097054451303 | | 1985 | 2.2102564199317 | | 1984 | 2.2327964154899 | | 1983 | 2.227116598772 | | 1982 | 2.2526203731831 | | 1981 | 2.2835055408641 | | 1980 | 2.2868585788486 | | 1979 | 2.2609074547966 | | 1978 | 2.1845107811176 | | 1977 | 2.1427633331707 | | 1976 | 2.0719498528079 | | 1975 | 1.9852737251226 | | 1974 | 1.9599830813457 | | 1973 | 1.9845831278752 | | 1972 | 2.0476867878981 | | 1971 | 2.1430525013569 | | 1970 | 2.2683895862776 | | 1969 | 2.3310136918808 | | 1968 | 2.3614783503939 | | 1967 | 2.4977221592071 | | 1966 | 2.7366707771014 | | 1965 | 2.8792418455056 | | 1964 | 2.918989003476 | | 1963 | 2.9688896109171 | | 1962 | 2.9745206537125 | | 1961 | 2.9797788494562 |
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