1971

6.4

1981

6.5

2006

7.5

2003

6.3

1983

5.9

2006

5.5

2000

6.3

1995

6.0

1987

6.2

1995

5.2

2005

6.1

2008

6.2

1978

4.2

1973

6.2

1964

6.5

2005

6.7

1971

5.2

1957

5.2

2001

5.9

1932

0.0