| Year | Value | | 2022 | 1.418278461694 | | 2021 | 1.391202419973 | | 2020 | 1.370695684642 | | 2019 | 1.385484725229 | | 2018 | 1.4051047225699 | | 2017 | 1.4188062846921 | | 2016 | 1.4287473963457 | | 2015 | 1.43794002441 | | 2014 | 1.4487047917708 | | 2013 | 1.4612951764715 | | 2012 | 1.470883000514 | | 2011 | 1.4717486887592 | | 2010 | 1.4638532507888 | | 2009 | 1.4469135166432 | | 2008 | 1.4217078710387 | | 2007 | 1.3942968010358 | | 2006 | 1.3680048606509 | | 2005 | 1.2629191957126 | | 2004 | 1.1795695481415 | | 2003 | 1.2106666182081 | | 2002 | 1.2675917470791 | | 2001 | 1.3482580034909 | | 2000 | 1.4419453422561 | | 1999 | 1.5028768275075 | | 1998 | 1.5924532562536 | | 1997 | 1.7216733735243 | | 1996 | 1.8976647458168 | | 1995 | 2.0684816948053 | | 1994 | 2.1541818424195 | | 1993 | 2.2229761685025 | | 1992 | 2.2819756555178 | | 1991 | 2.3254755155132 | | 1990 | 2.3542994078324 | | 1989 | 2.3560831690943 | | 1988 | 2.3030693827073 | | 1987 | 2.2955066966725 | | 1986 | 2.3371360303315 | | 1985 | 2.3808205782 | | 1984 | 2.4767659609609 | | 1983 | 2.6201962579219 | | 1982 | 2.7361053878678 | | 1981 | 2.8161971715129 | | 1980 | 2.73116665592 | | 1979 | 2.7045306185363 | | 1978 | 2.9144510010296 | | 1977 | 3.048146373366 | | 1976 | 3.100827856174 | | 1975 | 3.1371026219524 | | 1974 | 3.1721172511249 | | 1973 | 3.010672667691 | | 1972 | 3.0303003257093 | | 1971 | 3.2481717772634 | | 1970 | 3.2480706854363 | | 1969 | 3.2349772924793 | | 1968 | 3.2062247479357 | | 1967 | 3.1587857116368 | | 1966 | 3.1133569573938 | | 1965 | 3.0772423386731 | | 1964 | 3.0539692778475 | | 1963 | 3.0406272823778 | | 1962 | 3.0338563548679 | | 1961 | 3.0239647420388 |
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