| Year | Value | | 2020 | 0.2715290889113 | | 2019 | 1.3764483523708 | | 2018 | 0.28596499682526 | | 2017 | 0.29483556201719 | | 2016 | 0.28141864715978 | | 2015 | 0.2900944802911 | | 2014 | 0.29900818983432 | | 2009 | 0.24803245414408 | | 2008 | 0.26064183463318 | | 2007 | 0.26743556738215 | | 2005 | 0.28156040181929 | | 2004 | 0.27366274320446 | | 1999 | 0.25461467887572 | | 1998 | 0.26175886250069 | | 1997 | 0.27111737773826 | | 1996 | 0.28199188540151 | | 1995 | 0.29383959414092 | | 1994 | 0.30613781834761 | | 1993 | 0.3192462723209 | | 1992 | 0.33316859997002 | | 1991 | 0.3477809258392 |
|