| Year | Value | | 2022 | 1.3543893401962 | | 2021 | 1.536340380888 | | 2020 | 1.429790701133 | | 2019 | 1.3746963143305 | | 2018 | 1.3402596391912 | | 2017 | 1.2370678817014 | | 2016 | 1.5411029613838 | | 2015 | 1.3265583963164 | | 2014 | 1.3076866415984 | | 2013 | 1.4411210633838 | | 2012 | 1.4058599486954 | | 2011 | 1.4917984786847 | | 2010 | 1.4882180317251 | | 2009 | 1.5340637662137 | | 2008 | 1.4159467462429 | | 2007 | 1.3779081019748 | | 2006 | 1.5120852329606 | | 2005 | 1.5937918031344 | | 2004 | 1.5048739869189 | | 2003 | 1.4326934081195 | | 2002 | 1.4640202324097 | | 2001 | 1.4445031717197 | | 2000 | 1.4064679631307 | | 1999 | 1.4258424848436 | | 1998 | 1.4226122876212 | | 1997 | 1.5411569209307 | | 1996 | 1.6016439289538 | | 1995 | 1.7069898561593 | | 1994 | 1.6812127583871 | | 1993 | 1.7865070658018 | | 1992 | 1.8052441000228 | | 1991 | 1.8299547816599 | | 1990 | 1.840828125429 | | 1989 | 1.8875026444676 | | 1988 | 1.8854264664633 | | 1987 | 1.8593020777788 | | 1986 | 1.9158254528648 | | 1985 | 1.843543375764 | | 1984 | 1.8613234071293 | | 1983 | 1.9092767397199 | | 1982 | 2.0351335405457 | | 1981 | 2.0026738390806 | | 1980 | 2.0267249105433 | | 1979 | 2.0286208683968 | | 1978 | 2.0938850145042 | | 1977 | 2.0702088466903 | | 1976 | 2.3583469532379 | | 1975 | 3.0951080556011 | | 1974 | 4.3422798585462 | | 1973 | 3.4795625646625 | | 1972 | 4.0610442364291 | | 1971 | 4.3317658385887 | | 1970 | 4.1378806775846 | | 1969 | 4.1390166163036 | | 1968 | 4.5028155800862 | | 1967 | 4.4637901851444 | | 1966 | 3.8528957405825 | | 1965 | 3.8136131460626 | | 1964 | 4.111497258189 | | 1963 | 3.9557892185861 | | 1962 | 4.2266736473583 | | 1961 | 3.8875017903093 | | 1960 | 2.5556707902849 |
|