| Year | Value | | 2022 | 1.3958131977543 | | 2021 | 1.5997674680295 | | 2020 | 1.5893255862118 | | 2019 | 1.4352992586088 | | 2018 | 1.4558831523683 | | 2017 | 1.4048380780238 | | 2016 | 1.1037929021716 | | 2015 | 0.91014731012073 | | 2014 | 1.53977309916 | | 2013 | 1.3867774478536 | | 2012 | 1.4909616940382 | | 2011 | 1.6104039181111 | | 2010 | 1.6051289407531 | | 2009 | 1.7865792568122 | | 2008 | 1.5209528101396 | | 2007 | 2.2370999984712 | | 2006 | 1.6085990171171 | | 2005 | 1.3235946142231 | | 2004 | 1.5838759525399 | | 2003 | 1.4865008742033 | | 2002 | 1.5485667306433 | | 2001 | 1.8245836904164 | | 2000 | 1.7562434184138 | | 1999 | 1.1318063432343 | | 1998 | 1.2591888659573 | | 1997 | 1.3649595807619 | | 1996 | 1.4242463450111 | | 1995 | 1.6257873899244 | | 1994 | 1.7026372729919 | | 1993 | 1.8085593191165 | | 1992 | 1.8404141065121 | | 1991 | 2.1667882538423 | | 1990 | 2.1087552598472 | | 1989 | 2.2701066324874 | | 1988 | 2.0520150894125 | | 1987 | 1.96952748393 | | 1986 | 1.0439617542777 | | 1985 | 1.1331579245067 | | 1984 | 1.2226079348416 | | 1983 | 1.2414208411213 | | 1982 | 1.1549677985711 | | 1981 | 0.91942050942146 | | 1980 | 0.86205143844668 | | 1979 | 0.93885694167351 | | 1978 | 0.87309500071215 | | 1977 | 0.50757575757576 | | 1976 | 0.39615076182839 | | 1975 | 0.30049786628734 | | 1974 | 0.24222222222222 | | 1973 | 0.21874076263671 | | 1972 | 0.24885145482389 | | 1971 | 0.21708352996697 | | 1970 | 0.18769551616267 |
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