1997

7.5

2003

5.5

2006

5.6

2006

7.5

1990

7.4

2000

7.1

1991

7.6

1973

6.9

1994

6.7

2004

1.4

1986

7.0

2003

6.9

2008

6.7

2002

6.5

2007

7.1

2006

5.4

1985

8.1

1979

5.8

1968

4.2

1993

6.2