1988

7.8

2001

7.4

2003

7.1

2003

6.7

1988

7.2

2005

6.8

1982

7.5

1985

6.7

2005

6.7

1991

6.3

1999

6.2

1981

6.5

1968

4.9

2007

6.8

1984

6.3

1956

6.5

2006

7.0

2004

7.0

2009

5.7

1987

6.0