Year | Value | 2017 | 2.232 | 2016 | 2.043 | 2015 | 2.067 | 2011 | 1.659 | 2010 | 2.114 | 2009 | 1.602 | 2003 | 1.505 | 2002 | 1.575 | 2001 | 1.552 | 2000 | 1.452 | 1999 | 1.376 | 1998 | 1.313 | 1997 | 1.324 | 1996 | 1.307 | 1995 | 1.234 | 1994 | 1.258 | 1993 | 1.091 | 1992 | 1.178 | 1991 | 1.142 | 1990 | 0.936 | 1977 | 0.637 | 1975 | 0.351 | 1970 | 0.348 | 1965 | 0.335 | 1960 | 0.396 |
|