1992

6.7

2000

7.1

2006

6.1

1968

5.9

1989

8.3

1985

5.3

2005

8.8

2003

8.6

1993

6.5

1992

6.8

1973

5.4

2000

6.2

1993

8.0

2004

8.3

2004

8.6

1990

8.6

2007

6.8

2003

7.7

1977

7.3

2006

7.5