6.4

1981

6.2

2013

6.1

1991

5.9

2006

7.0

1990

6.5

1986

6.8

1976

5.9

2003

7.2

2010

7.1

2016

7.9

2005

5.4

1975

4.5

2009

7.3

2003

6.1

5.0

2004

5.6

1993

7.6

2012

6.1

2011

7.2