| Year | Value | | 2022 | 0.83308238204777 | | 2021 | 1.218203729303 | | 2020 | 1.7640683768735 | | 2019 | 1.9081926589147 | | 2018 | 2.0286376612478 | | 2017 | 2.1075830171014 | | 2016 | 2.1825071025343 | | 2015 | 2.2446364495981 | | 2014 | 2.2875898831972 | | 2013 | 2.3499412828226 | | 2012 | 2.4353240004375 | | 2011 | 2.5885387384378 | | 2010 | 2.7599336999598 | | 2009 | 2.8519648041138 | | 2008 | 2.929652808845 | | 2007 | 3.0056236957452 | | 2006 | 3.0559572683577 | | 2005 | 3.1324222113556 | | 2004 | 3.1949592365016 | | 2003 | 3.2580096059719 | | 2002 | 3.3579972230607 | | 2001 | 3.4595580118374 | | 2000 | 3.4973353815057 | | 1999 | 3.5834886061873 | | 1998 | 3.7728877134313 | | 1997 | 3.9705386084453 | | 1996 | 4.156070094 | | 1995 | 4.3108512063169 | | 1994 | 4.4917730294359 | | 1993 | 4.6367839033654 | | 1992 | 4.7744576453932 | | 1991 | 4.9216370564041 | | 1990 | 4.4748701136427 | | 1989 | 3.816694519312 | | 1988 | 3.74690340133 | | 1987 | 3.8882742102917 | | 1986 | 4.0549823106897 | | 1985 | 4.2165974251811 | | 1984 | 4.3051267500414 | | 1983 | 4.402684867916 | | 1982 | 4.5048973178147 | | 1981 | 4.5945688060955 | | 1980 | 4.3139492660618 | | 1979 | 3.9352606085721 | | 1978 | 4.0832579275033 | | 1977 | 4.4644232197315 | | 1976 | 4.7093347797727 | | 1975 | 5.0030872620657 | | 1974 | 5.282711707805 | | 1973 | 5.4924831271115 | | 1972 | 5.7757916270901 | | 1971 | 5.3962282397073 | | 1970 | 3.3989947729346 | | 1969 | 1.9839952420609 | | 1968 | 2.1264470742243 | | 1967 | 2.1203669704101 | | 1966 | 2.1129034496755 | | 1965 | 2.0930745765692 | | 1964 | 2.0598844760136 | | 1963 | 2.0918441572099 | | 1962 | 1.9857180437772 | | 1961 | 1.7896261009324 |
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