| Year | Value | | 1998 | 70.338983050848 | | 1997 | 76.851851851852 | | 1996 | 79.120879120879 | | 1995 | 69.89247311828 | | 1994 | 64.761904761905 | | 1993 | 77.215189873418 | | 1991 | 75 | | 1990 | 76.829268292683 | | 1989 | 77.380952380952 | | 1988 | 77.464788732394 | | 1987 | 75.949367088608 | | 1986 | 55.045871559633 | | 1985 | 48.8 | | 1984 | 33.333333333333 | | 1983 | 40.609137055838 | | 1982 | 40.654205607477 | | 1981 | 26.436781609195 | | 1980 | 25.837320574163 | | 1979 | 30.872483221477 | | 1978 | 13.888888888889 | | 1977 | 21.92513368984 | | 1974 | 1.4446227929374 | | 1973 | 2.0100502512563 | | 1972 | 1.6423357664234 |
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