| Year | Value | | 2014 | 1.363692 | | 2013 | 1.440588 | | 2012 | 1.275841047 | | 2011 | 1.52106019 | | 1991 | 5 | | 1990 | 8.6999998093 | | 1989 | 7.9000000954 | | 1988 | 4.4000000954 | | 1987 | 3.9000000954 | | 1986 | 3.5 | | 1985 | 3.2999999523 | | 1984 | 3.9000000954 | | 1983 | 3.9000000954 | | 1982 | 4.0999999046 | | 1981 | 3.4000000954 | | 1980 | 0.5 | | 1979 | 0.400000006 | | 1978 | 0.3000000119 | | 1977 | 0.3000000119 | | 1976 | 0.200000003 | | 1975 | 0.200000003 | | 1974 | 0.200000003 | | 1973 | 0.200000003 | | 1972 | 0.200000003 | | 1971 | 0.1000000015 | | 1970 | 0.1000000015 |
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