1974

5.8

1990

6.0

1997

6.4

2009

7.0

1971

6.8

1997

4.5

2004

7.3

1995

7.3

2014

6.1

2005

6.3

2010

6.6

2013

6.5

2007

6.7

2006

6.9

1998

6.6

2000

6.8

2008

6.3

2013

7.4

1988

6.2

2009

6.7