| Year | Value | | 2022 | 1.4044899935946 | | 2021 | 1.3493239658232 | | 2020 | 1.3086248099013 | | 2019 | 1.3879072747944 | | 2018 | 1.4603266853342 | | 2017 | 1.3879225384237 | | 2016 | 1.7089170362204 | | 2015 | 1.4376546156851 | | 2014 | 1.7109375971182 | | 2013 | 2.0313845551028 | | 2012 | 2.3062703783852 | | 2011 | 2.6209697739344 | | 2010 | 2.7489139609035 | | 2009 | 2.8470047848342 | | 2008 | 13.78021978022 | | 2007 | 16.339998132335 | | 2006 | 20.142148917647 | | 2005 | 23.406181496688 | | 2004 | 25.13750850919 | | 2003 | 24.970522028084 | | 2002 | 27.073934894661 | | 2001 | 31.202575191665 | | 2000 | 33.416855394401 | | 1999 | 32.598373628773 | | 1998 | 38.48125 | | 1997 | 39.495256059338 | | 1996 | 41.664114865095 | | 1995 | 43.980847548963 | | 1994 | 45.90726617535 | | 1993 | 44.944122020241 | | 1992 | 43.28484015984 | | 1991 | 46.810878716417 | | 1990 | 47.789951862893 | | 1989 | 45.684884381824 | | 1988 | 47.757007654585 | | 1987 | 47.615074398554 | | 1986 | 49.141992404991 | | 1985 | 45.462746408286 | | 1984 | 41.456452706319 | | 1983 | 40.595115945003 | | 1982 | 35.292310842633 | | 1981 | 39.331519626895 | | 1980 | 39.987511707774 | | 1979 | 36.884270643293 | | 1978 | 37.196935556557 | | 1977 | 32.537981172523 | | 1976 | 27.522451135763 | | 1975 | 28.454545454545 | | 1974 | 32.196452933151 | | 1973 | 34.217252396166 |
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