1941

3.7

1965

4.8

1971

7.2

2005

6.7

1991

5.7

2003

5.9

1996

5.5

2002

6.2

1975

5.4

2006

6.5

2003

4.1

2014

6.6

1986

6.0

1960

6.9

2001

6.0

2007

5.2

2008

6.7

1972

5.4

1948

7.0

1994

6.5