1990

6.2

1991

6.8

1992

6.2

2008

6.9

2006

4.7

1971

7.2

1993

6.3

1981

7.1

2008

6.6

1985

6.4

1986

5.8

1999

6.8

1994

5.8

2001

6.9

1997

6.8

1997

6.9

1932

7.4

1978

7.6

2000

6.1

2002

7.2