1934

4.1

1985

7.1

2006

7.0

1990

7.7

1966

7.1

1999

7.1

2006

5.8

2001

6.4

1990

6.9

2001

7.3

2003

7.1

2002

6.2

1997

6.8

1960

7.2

1975

6.9

1981

7.5

2004

6.3

2006

5.4

1956

6.5

2007

7.6