1976

6.5

1999

7.1

1981

7.1

2001

6.2

1960

7.3

1991

7.3

1995

7.3

1996

7.6

2001

7.0

2006

7.9

1956

6.5

2000

6.8

2004

6.5

2004

6.1

1998

7.3

1999

6.8

1970

6.1

1971

6.4

1972

6.2

1973

5.7