1997

6.9

2003

6.2

2000

7.2

2004

7.1

2005

7.1

1996

7.3

1989

5.9

2006

5.8

2007

6.6

2000

6.7

2005

6.0

1994

5.2

2000

6.5

1976

7.1

1974

7.4

2000

6.9

2009

6.5

2011

7.2

1955

7.3

2009

6.6