1990

6.2

1991

6.8

1992

6.2

2006

4.7

1971

7.2

1993

6.3

1981

7.1

1999

7.2

2008

6.6

1999

6.8

1994

5.8

1997

6.8

1984

6.5

1997

6.9

1978

7.6

2000

6.1

2002

7.2

1971

7.4

1954

7.9

2007

6.2