1993

6.3

1991

6.7

1984

6.0

2002

6.2

1997

6.8

2005

6.7

1973

7.4

1998

5.5

2005

7.0

1992

6.8

1971

7.0

2004

7.2

2005

6.2

1990

6.7

2007

6.5

2002

5.3

2001

7.5

2008

6.5

2002

2.0

2011

1.0