| Year | Value | | 2014 | 15.479576301383 | | 2013 | 7.6393308482589 | | 2012 | 3.745603827192 | | 2008 | 1.4898510813043 | | 2007 | 0.94667751725465 | | 2006 | 1.120335406486 | | 2005 | 1.5281111599446 | | 2004 | 2.0710744567484 | | 2003 | 2.0720480715153 | | 2002 | 2.0692385202246 | | 2001 | 2.4135078584984 | | 2000 | 3.146863673581 | | 1999 | 3.7838602447132 | | 1998 | 5.2974415319416 | | 1997 | 4.078026715669 | | 1982 | 2.2405257767156 | | 1981 | 1.755113763283 | | 1980 | 2.9223643581826 | | 1979 | 3.2207494264593 | | 1978 | 3.7992264416315 | | 1977 | 2.4639944473365 | | 1976 | 1.9686162624822 | | 1975 | 2.2539682539682 | | 1974 | 3.2912696368787 | | 1973 | 3.9848619768477 | | 1972 | 3.7096774193548 | | 1971 | 5.3226797787339 | | 1970 | 6.0729312762973 | | 1969 | 3.7628865979381 | | 1968 | 2.85594639866 | | 1967 | 3.3609467455621 | | 1966 | 2.9149232914923 | | 1965 | 1.8571428571429 | | 1964 | 1.84375 | | 1963 | 2.4079422382671 | | 1962 | 3.1041666666667 | | 1961 | 1.8550724637681 | | 1960 | 1.592 |
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