| Year | Value | | 2022 | 33.9572632404 | | 2021 | 36.051263815103 | | 2020 | 37.190099984721 | | 2019 | 36.353496093976 | | 2018 | 35.45878774154 | | 2017 | 35.284839403985 | | 2016 | 37.280060803025 | | 2015 | 36.733774227122 | | 2014 | 37.779293739976 | | 2013 | 39.745930837043 | | 2012 | 40.595891051537 | | 2011 | 38.057232575639 | | 2010 | 38.781471021896 | | 2009 | 38.976119814871 | | 2008 | 37.382532868972 | | 2007 | 36.317434616088 | | 2006 | 35.338504471244 | | 2005 | 32.362678501922 | | 2004 | 31.577400668177 | | 2003 | 30.164596698861 | | 2002 | 30.749176431082 | | 2001 | 28.422290432944 | | 2000 | 27.797457690457 | | 1999 | 26.659956815379 | | 1998 | 25.834054726152 | | 1997 | 24.397478698652 | | 1996 | 23.1387940832 | | 1995 | 22.146154490518 | | 1994 | 22.417160059285 | | 1993 | 20.901202135505 | | 1992 | 21.994003830075 | | 1991 | 22.560405924653 | | 1990 | 23.024411863471 | | 1989 | 22.34616801455 | | 1988 | 22.195895840523 | | 1987 | 22.625377191496 | | 1986 | 22.776064567848 | | 1985 | 21.52029364293 | | 1984 | 16.294890536618 | | 1983 | 23.099539721043 | | 1982 | 23.528482246807 | | 1981 | 21.143182052384 | | 1980 | 8.3329313136296 | | 1979 | 7.0762815155028 | | 1978 | 5.70444354275 | | 1977 | 10.039922606744 | | 1976 | 0.84090661599576 |
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