| Year | Value | | 2013 | 1.19358 | | 2012 | 5.4487094452797 | | 2011 | 9.1155138964507 | | 2010 | 8.328779694 | | 2001 | 7.364 | | 2000 | 12.273 | | 1999 | 13.6999998093 | | 1998 | 13.5 | | 1997 | 15.3000001907 | | 1996 | 16.3999996185 | | 1995 | 15.3000001907 | | 1994 | 14.3999996185 | | 1993 | 14.1999998093 | | 1992 | 15.1999998093 | | 1986 | 0.8000000119 | | 1985 | 0.6999999881 | | 1984 | 0.6000000238 | | 1983 | 0.6000000238 | | 1982 | 0.6000000238 | | 1981 | 0.5 | | 1980 | 0.5 | | 1979 | 0.5 | | 1978 | 0.5 | | 1977 | 0.5 | | 1976 | 0.8000000119 | | 1975 | 1.2000000477 | | 1974 | 1.6000000238 | | 1973 | 1.7000000477 | | 1972 | 2.2000000477 | | 1971 | 2.4000000954 | | 1970 | 2.4000000954 |
|