| Year | Value | | 2021 | 1.16 | | 2020 | 1.217 | | 2019 | 1.228 | | 2018 | 1.301 | | 2017 | 1.374 | | 2016 | 1.466 | | 2015 | 1.506 | | 2014 | 1.498 | | 2013 | 1.506 | | 2012 | 1.531 | | 2011 | 1.459 | | 2010 | 1.443 | | 2009 | 1.473 | | 2008 | 1.458 | | 2007 | 1.345 | | 2006 | 1.31 | | 2005 | 1.213 | | 2004 | 1.218 | | 2003 | 1.172 | | 2002 | 1.095 | | 2001 | 1.078 | | 2000 | 1.116 | | 1999 | 1.127 | | 1998 | 1.211 | | 1997 | 1.272 | | 1996 | 1.335 | | 1995 | 1.398 | | 1994 | 1.468 | | 1993 | 1.562 | | 1992 | 1.674 | | 1991 | 1.776 | | 1990 | 1.85 | | 1989 | 1.935 | | 1988 | 2.02 | | 1987 | 2.05 | | 1986 | 2.08 | | 1985 | 2.06 | | 1984 | 2.09 | | 1983 | 2.08 | | 1982 | 1.98 | | 1981 | 1.93 | | 1980 | 1.95 | | 1979 | 1.96 | | 1978 | 1.96 | | 1977 | 1.94 | | 1976 | 1.99 | | 1975 | 2.02 | | 1974 | 2.04 | | 1973 | 2.04 | | 1972 | 2.08 | | 1971 | 2.12 | | 1970 | 2.09 | | 1969 | 2.04 | | 1968 | 1.998 | | 1967 | 2.01 | | 1966 | 2.02 | | 1965 | 1.99 | | 1964 | 1.96 | | 1963 | 2.06 | | 1962 | 2.14 | | 1961 | 2.17 | | 1960 | 2.24 |
|