1997

6.8

2005

6.7

1999

6.9

2004

6.3

2005

7.4

2006

6.3

1972

3.7

2004

7.2

2006

7.0

2003

6.7

2003

6.0

2005

5.9

1979

7.8

2001

6.7

2002

7.1

2006

6.5

1971

4.8

1975

3.3

2003

5.0

1970

3.0