| Year | Value | | 2022 | 6.500205652723 | | 2021 | 6.4523551123317 | | 2010 | 1.4739090832174 | | 2009 | 1.9922131769227 | | 2008 | 2.0105009271132 | | 2007 | 1.9598415997188 | | 2006 | 1.7505076485718 | | 2005 | 1.9930162686392 | | 2004 | 2.4338596855738 | | 2003 | 3.3339948402461 | | 2002 | 3.9299699222519 | | 1991 | 13.011254789272 | | 1990 | 10.743878769782 | | 1989 | 13.077574525745 | | 1988 | 16.272350880386 | | 1987 | 15.889533417402 | | 1985 | 24.84641485847 | | 1984 | 12.733925143954 | | 1983 | 13.958483372167 | | 1982 | 19.277386753294 | | 1981 | 12.216801824632 | | 1980 | 7.8686808777867 |
|