1997

6.1

1996

5.9

1991

5.3

1994

4.7

1990

7.2

1951

7.5

1996

5.8

1989

7.3

1968

6.9

1966

6.9

1993

6.1

1990

6.0

1998

6.6

2003

5.0

1988

7.3

1996

8.0

1939

7.5

2005

8.4

1972

6.9

2004

6.0