1971    87.9
   1972    88.5
   1973    88.8
   1974    90.2
   1975    78.1
   1976    79.6
   1977    81.5
   1978    82.4
   1979    80.5
   1980    77.7
   1981    76.7
   1982    73.2
   1983    69.3
   1984    72.2
   1985    76.0
   1986    73.3
   1987    75.0
   1988    75.5
   1989    77.6
   1990    75.9