| Year | Value | | 2021 | 0.786 | | 2020 | 0.752 | | 2019 | 0.735 | | 2018 | 0.701 | | 2017 | 0.669 | | 2010 | 1.263 | | 2009 | 1.256 | | 2008 | 1.251 | | 2007 | 1.242 | | 2006 | 1.236 | | 2005 | 1.23 | | 2004 | 1.109 | | 2003 | 1.227 | | 2002 | 1.112 | | 2001 | 1.221 | | 2000 | 1.219 | | 1997 | 1.24 | | 1996 | 1.23 | | 1992 | 0.108 | | 1990 | 0.119 | | 1989 | 0.124 | | 1985 | 0.154 | | 1984 | 0.154 | | 1981 | 0.15 | | 1980 | 0.128 | | 1975 | 0.113 | | 1970 | 0.111 | | 1960 | 0.146 |
|