| Year | Value | | 2022 | 1.9230282182075 | | 2021 | 2.0285605403896 | | 2020 | 2.1476322735763 | | 2019 | 2.26018781067 | | 2018 | 2.325313321969 | | 2017 | 2.3941125596752 | | 2016 | 2.468594345058 | | 2015 | 2.5432006629564 | | 2014 | 2.6156952303367 | | 2013 | 2.6928825358423 | | 2012 | 2.7779904526874 | | 2011 | 2.9029896147066 | | 2010 | 3.0035267026746 | | 2009 | 3.0478162226257 | | 2008 | 3.086113991493 | | 2007 | 3.1236611137206 | | 2006 | 3.1712878659514 | | 2005 | 3.2156031499028 | | 2004 | 3.2655294396826 | | 2003 | 3.3112340723959 | | 2002 | 3.349559561267 | | 2001 | 3.3945550997926 | | 2000 | 3.4521329401203 | | 1999 | 3.4908939079866 | | 1998 | 3.5330987615507 | | 1997 | 3.5821194627943 | | 1996 | 3.6049421586965 | | 1995 | 3.6338930772408 | | 1994 | 3.6627870280824 | | 1993 | 3.6771996535265 | | 1992 | 3.5844257834369 | | 1991 | 3.2086135735766 | | 1990 | 2.6442460651587 | | 1989 | 2.2694066132607 | | 1988 | 2.1788792025806 | | 1987 | 2.1740062941715 | | 1986 | 2.1616810180806 | | 1985 | 2.1435452338095 | | 1984 | 2.120070265126 | | 1983 | 2.092555854731 | | 1982 | 2.0671415940612 | | 1981 | 2.0493680019565 | | 1980 | 2.0462458411273 | | 1979 | 2.0691900659496 | | 1978 | 2.103931347377 | | 1977 | 2.1386793517809 | | 1976 | 2.1725368523532 | | 1975 | 2.2125174945921 | | 1974 | 2.2633280112203 | | 1973 | 2.3262761828502 | | 1972 | 2.3793688976796 | | 1971 | 2.391996822911 | | 1970 | 2.3634118145691 | | 1969 | 2.3123288267383 | | 1968 | 2.2439837423099 | | 1967 | 2.2271479736908 | | 1966 | 2.1948207810583 | | 1965 | 2.1271103180533 | | 1964 | 2.1460038056889 | | 1963 | 2.2157788257891 | | 1962 | 2.2772881010668 | | 1961 | 2.4871611274864 |
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