1990

7.8

2002

7.5

2007

8.5

1999

7.4

1995

7.2

2006

8.2

2012

8.6

1999

8.2

1982

8.3

2004

8.2

1992

8.5

1998

7.9

1992

6.8

2010

8.0

2009

8.7

2012

7.7

1986

7.7

1979

7.3

1975

7.0

2014

7.7