1979

6.7

2005

6.5

1989

6.2

1990

5.8

1997

6.1

1997

6.6

2005

6.5

1991

6.8

2004

6.6

1992

6.8

1988

7.1

2015

6.3

1973

3.7

1995

7.6

2000

8.2

1998

7.3

2000

7.3

1965

6.3

2000

5.9

1999

7.5