| Year | Value | | 2023 | 0.4970875972399 | | 2022 | 0.59668834586995 | | 2021 | 0.38203217521266 | | 2020 | 0.11178257414313 | | 2019 | 0.13410946235855 | | 2018 | 0.10172385775276 | | 2017 | 0.066117510188154 | | 2016 | 0.031221096348239 | | 2015 | 0.013271918202012 | | 2014 | 0.019715953686468 | | 2013 | 0.052725108136232 | | 2012 | 0.099276734210636 | | 2011 | 0.32568566171005 | | 2010 | 0.71718199961532 | | 2009 | 0.95008536036331 | | 2008 | 1.0355515102331 | | 2007 | 1.1068915081713 | | 2006 | 1.1504026576258 | | 2005 | 1.1913234413198 | | 2004 | 1.2567955819468 | | 2003 | 1.3477032111289 | | 2002 | 1.4564510654475 | | 2001 | 1.5271583233026 | | 2000 | 1.5109707398467 | | 1999 | 1.5198255316601 | | 1998 | 1.6012590836575 | | 1997 | 1.6815812275736 | | 1996 | 1.7725088767802 | | 1995 | 1.9017102711588 | | 1994 | 2.0348082542325 | | 1993 | 2.1499985793337 | | 1992 | 2.2697603322646 | | 1991 | 2.4100722558058 | | 1990 | 2.0519239734207 | | 1989 | 1.4994829883842 | | 1988 | 1.3971276309183 | | 1987 | 1.4064215904602 | | 1986 | 1.4141046331448 | | 1985 | 1.4089844178863 | | 1984 | 1.4264553598485 | | 1983 | 1.470838505429 | | 1982 | 1.4769331549434 | | 1981 | 1.3960208104673 | | 1980 | 1.1889103779797 | | 1979 | 1.0487378756123 | | 1978 | 1.0534596876679 | | 1977 | 1.0860012662406 | | 1976 | 1.1727708843281 | | 1975 | 1.0772321251122 |
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