1981

5.2

1986

5.1

1993

4.9

1996

3.7

1968

7.1

1976

4.3

1978

7.2

1995

7.3

1979

6.7

1994

3.2

1998

4.0

1988

6.6

1989

3.8

1983

7.5

1998

4.6

1979

8.0

1998

6.9