1987

7.5

2000

5.3

2006

7.2

1999

6.6

2005

7.5

1992

6.9

2006

6.5

2007

6.7

2004

6.6

1992

7.1

2007

7.9

1973

6.1

2007

6.3

2009

7.4

1999

6.5

1995

7.1

2002

6.0

2003

6.0

2001

6.6

2003

6.3