| Year | Value | | 2022 | 5.0878876079285 | | 2021 | 2.4983333333334 | | 2020 | 0.53728802341174 | | 2019 | 0.38300030360814 | | 2018 | 1.4758393500264 | | 2017 | 1.9443323078637 | | 2016 | 0.97168573991217 | | 2015 | 0.70633177245575 | | 2014 | 1.2747744640132 | | 2013 | 1.3013475454741 | | 2012 | 2.1870710443331 | | 2011 | 4.0259650043609 | | 2010 | 2.9392865265569 | | 2009 | 2.7564965449393 | | 2008 | 4.6738965553341 | | 2007 | 2.5345738213793 | | 2006 | 2.2423402851892 | | 2005 | 2.7537916273504 | | 2004 | 3.5906629888258 | | 2003 | 3.5148745145994 | | 2002 | 2.762262102966 | | 2001 | 4.0665758789779 | | 2000 | 2.2591658008016 | | 1999 | 0.81295725444637 | | 1998 | 7.5135800807931 | | 1997 | 4.4389318457463 | | 1996 | 4.9245435429275 | | 1995 | 4.4807410855725 | | 1994 | 6.2658595003968 | | 1993 | 4.8009966021535 | | 1992 | 6.2132814635518 | | 1991 | 9.3327904816149 | | 1990 | 8.5732722572868 | | 1989 | 5.700165445614 | | 1988 | 7.1460977372161 | | 1987 | 3.0496607708742 | | 1986 | 2.7499809606336 | | 1985 | 2.4591087921527 | | 1984 | 2.2739564000186 | | 1983 | 3.4206141949892 | | 1982 | 7.1908466400687 | | 1981 | 21.351640254 | | 1980 | 28.697608636202 | | 1979 | 18.323496342179 | | 1978 | 14.460285019502 | | 1977 | 10.096665331339 | | 1976 | 15.327320521319 | | 1975 | 25.249256405673 | | 1974 | 24.30419954024 | | 1973 | 3.2210290469233 | | 1972 | 11.688986680685 | | 1971 | 13.511702331308 | | 1970 | 15.950342364694 | | 1969 | 12.389564711119 | | 1968 | 10.771821396935 | | 1967 | 10.882440057196 | | 1966 | 11.261384877581 | | 1965 | 13.548194710465 | | 1964 | 29.46283145008 | | 1963 | 20.691647318648 | | 1962 | 6.6183109749239 | | 1961 | 8.1956528825409 | | 1960 | 7.9655657548259 |
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