| Year | Value | | 2002 | 0.00040416977919498 | | 2001 | 0.00016515311021723 | | 2000 | 0.0009884044861479 | | 1999 | 0.00063902709402988 | | 1998 | 0.0086448918631814 | | 1997 | 0.0058206111747826 | | 1996 | 0.0022678093808581 | | 1995 | 0.0049788663377991 | | 1994 | 0.021856558528741 | | 1993 | 0.084515969996831 | | 1992 | 0.49847021210767 | | 1991 | 0.87351057965484 | | 1990 | 3.6364553386796 | | 1989 | 3.7932053175775 | | 1988 | 5.5880875722535 | | 1987 | 4.9274298513788 | | 1986 | 3.7947306331105 | | 1985 | 4.2265634598845 | | 1984 | 4.4367574071289 | | 1983 | 5.6740151788941 | | 1982 | 6.8802781917536 | | 1981 | 7.4202715503632 | | 1980 | 7.56 | | 1979 | 8.6447295036252 | | 1978 | 11.519078473722 | | 1977 | 14.594127806563 | | 1976 | 14.806110458284 | | 1975 | 15.106732348112 | | 1974 | 16.412213740458 | | 1973 | 18.352941176471 |
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