1991

6.8

1988

6.3

2006

6.1

2003

5.1

2018

6.3

2000

5.8

1981

6.4

1992

7.0

2007

6.5

1995

6.7

1971

5.2

2001

7.1

2004

6.4

1982

6.8

2006

6.0

2008

6.4

2007

6.6

2005

7.7

1988

7.2

1999

6.6