| Year | Value | | 1986 | 1.0439617542777 | | 1985 | 1.1331579245067 | | 1984 | 1.2226079348416 | | 1982 | 1.1549677985711 | | 1981 | 0.91942050942146 | | 1980 | 0.86205143844668 | | 1979 | 0.93885694167351 | | 1978 | 0.87309500071215 | | 1977 | 0.50757575757576 | | 1976 | 0.39615076182839 | | 1975 | 0.30049786628734 | | 1974 | 0.24222222222222 | | 1973 | 0.21874076263671 | | 1972 | 0.24885145482389 | | 1971 | 0.21708352996697 | | 1970 | 0.18769551616267 |
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