1988

6.1

1987

5.3

2009

5.6

2001

6.9

1997

5.6

2011

6.4

2007

9.8

1995

6.3

1994

5.7

2002

6.1

1990

7.4

1999

5.1

2006

5.7

1980

6.7

2003

5.7

1997

6.7

2010

7.2

1989

7.0

2013

7.6

2016

7.0