1976

6.4

1999

7.0

1981

7.1

2007

6.9

2005

6.7

1991

6.3

1991

7.3

1995

7.3

2002

6.6

2004

6.3

1999

8.2

2003

7.1

2003

6.7

1974

6.0

1970

6.2

1971

6.4

1972

6.2

1973

5.7

1966

7.1

1971

6.4