1981

6.6

2001

5.1

2014

4.6

2017

4.7

2008

6.1

1964

6.8

1985

5.3

2007

6.3

1990

6.4

1986

6.3

1988

5.5

1989

5.0

2008

4.8

1981

7.4

2004

7.3

1922

7.7

1978

7.6

1996

7.0

2000

6.1

2006

6.8