| Year | Value | | 2022 | 43.222564537548 | | 2021 | 42.498281632256 | | 2020 | 40.823318299242 | | 2019 | 41.102543716667 | | 2018 | 41.746229587586 | | 2017 | 46.103476522048 | | 2016 | 44.848711245383 | | 2015 | 44.046215309175 | | 2014 | 47.295047799475 | | 2013 | 45.515697106272 | | 2012 | 47.253102209669 | | 2011 | 48.809210900431 | | 2010 | 50.591580905801 | | 2009 | 43.863106021342 | | 2008 | 44.358468880678 | | 2007 | 49.970919838469 | | 2006 | 48.168520736073 | | 2005 | 43.62664151037 | | 2004 | 40.61435064574 | | 2003 | 39.398793615194 | | 2002 | 38.42802088916 | | 2001 | 40.081772000628 | | 2000 | 46.374863981682 | | 1999 | 48.912257726439 | | 1998 | 51.349608651383 | | 1997 | 52.300483379543 | | 1996 | 48.876762692708 | | 1995 | 50.59419121942 | | 1994 | 48.093738825666 | | 1993 | 44.36899966471 | | 1992 | 46.993176937452 | | 1991 | 44.974234807006 | | 1990 | 43.734682012254 | | 1989 | 42.763515647468 | | 1988 | 41.355008066478 | | 1987 | 37.854396099233 | | 1986 | 39.793761233723 | | 1985 | 41.567863353286 | | 1984 | 44.089853449045 | | 1983 | 41.581296046406 | | 1982 | 37.220302372945 | | 1981 | 35.857411333835 | | 1980 | 33.827907624168 | | 1979 | 35.448908060716 | | 1978 | 32.457711203194 | | 1977 | 30.199654025229 | | 1976 | 30.080346265187 | | 1975 | 29.655064923267 | | 1974 | 25.837395128159 | | 1973 | 25.358371056534 | | 1972 | 26.296241443167 |
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