1981

6.4

1990

5.5

2011

5.9

1997

6.5

2005

6.2

2004

6.7

1990

7.8

1995

6.2

2003

6.7

2004

6.2

1993

6.3

2009

4.5

1994

6.8

2003

6.9

1996

7.3

2003

5.1

1986

6.1

2001

7.6

2000

6.7

2001

5.6