1950

2.4

1951

4.7

1952

6.8

1953

7.4

1954

6.9

1955

6.2

1956

5.7

1957

5.3

1958

4.9

1959

4.4

1960

4.2

1961

4.1

1962

4.0

1963

3.6

1964

3.4

1965

2.9

1966

2.7

1967

2.7

1968

2.5

1969

2.3

1970

2.2

1971

2.1

1972

2.0

1973

1.8

1974

1.8

1975

1.9

1976

1.8

1977

1.8

1978

1.8

1979

1.7

1980

1.8

1981

1.7

1982

2.0

1983

2.1

1984

2.1

1985

2.1

1986

2.1

1987

2.1

1988

2.0

1989

1.9

1990

2.0

1991

1.9

1992

1.9

1993

1.8

1994

1.7

1995

1.6

1996

1.4

1997

1.2

1998

1.3

1999

1.2

2000

1.1

2001

1.1

2002

1.1

2003

1.1

2004

1.1

2005

1.1

2006

1.1

2007

1.2

2008

1.2

2009

1.4

2010

1.2

2011

1.2

2012

1.1

2013

1.0

2014

1.0

2015

1.2

2016

1.2

2017

1.3