1991

8.3

1996

7.8

1995

7.0

2003

6.5

1984

8.4

1993

7.5

2002

7.0

2006

5.4

1972

7.1

1954

7.9

1990

8.5

1947

5.9

1969

6.0

1973

7.4

2007

7.5

2003

6.3

1997

6.8

1997

6.9

2007

7.3

1999

6.4