1977

2.5

2006

3.5

1970

3.8

2001

3.8

2002

3.4

1999

3.2

1989

4.2

1975

5.1

2009

6.0

2002

5.0

2003

1.5

1996

4.7

1997

4.8

2000

5.7

1993

6.2

1976

4.0

2012

2.3

1972

6.4

2002

7.2

1982

6.3