| Year | Data | Change | Unit |
|---|---|---|---|
| 1950 | 6 | 0 | Percent |
| 1951 | 6 | 0 | Percent |
| 1952 | 6 | 0 | Percent |
| 1953 | 6 | 0 | Percent |
| 1954 | 6 | 0 | Percent |
| 1955 | 6 | 0 | Percent |
| 1956 | 6 | 0 | Percent |
| 1957 | 5.9 | -0.1 | Percent |
| 1958 | 5.9 | 0 | Percent |
| 1959 | 5.9 | 0 | Percent |
| 1960 | 5.9 | 0 | Percent |
| 1961 | 6 | + 0.1 | Percent |
| 1962 | 5.9 | -0.1 | Percent |
| 1963 | 5.9 | 0 | Percent |
| 1964 | 5.8 | -0.1 | Percent |
| 1965 | 5.8 | 0 | Percent |
| 1966 | 5.7 | -0.1 | Percent |
| 1967 | 5.7 | 0 | Percent |
| 1968 | 5.6 | -0.1 | Percent |
| 1969 | 5.6 | 0 | Percent |
| 1970 | 5.5 | -0.1 | Percent |
| 1971 | 5.5 | 0 | Percent |
| 1972 | 5.4 | -0.1 | Percent |
| 1973 | 5.4 | 0 | Percent |
| 1974 | 5.3 | -0.1 | Percent |
| 1975 | 5.3 | 0 | Percent |
| 1976 | 5.2 | -0.1 | Percent |
| 1977 | 5.2 | 0 | Percent |
| 1978 | 5.2 | 0 | Percent |
| 1979 | 5.1 | -0.1 | Percent |
| 1980 | 5.1 | 0 | Percent |
| 1981 | 5.1 | 0 | Percent |
| 1982 | 5 | -0.1 | Percent |
| 1983 | 5 | 0 | Percent |
| 1984 | 4.9 | -0.1 | Percent |
| 1985 | 4.9 | 0 | Percent |
| 1986 | 4.9 | 0 | Percent |
| 1987 | 4.8 | -0.1 | Percent |
| 1988 | 4.8 | 0 | Percent |
| 1989 | 4.8 | 0 | Percent |
| 1990 | 4.7 | -0.1 | Percent |
| 1991 | 4.7 | 0 | Percent |
| 1992 | 4.7 | 0 | Percent |
| 1993 | 4.7 | 0 | Percent |
| 1994 | 4.7 | 0 | Percent |
| 1995 | 4.7 | 0 | Percent |
| 1996 | 4.7 | 0 | Percent |
| 1997 | 4.7 | 0 | Percent |
| 1998 | 4.7 | 0 | Percent |
| 1999 | 4.6 | -0.1 | Percent |
| 2000 | 4.6 | 0 | Percent |
| 2001 | 4.6 | 0 | Percent |
| 2002 | 4.6 | 0 | Percent |
| 2003 | 4.6 | 0 | Percent |
| 2004 | 4.6 | 0 | Percent |
| 2005 | 4.6 | 0 | Percent |
| 2006 | 4.6 | 0 | Percent |
| 2007 | 4.5 | -0.1 | Percent |
| 2008 | 4.5 | 0 | Percent |
| 2009 | 4.5 | 0 | Percent |
| 2010 | 4.5 | 0 | Percent |
| 2011 | 4.5 | 0 | Percent |
| 2012 | 4.5 | 0 | Percent |
| 2013 | 4.4 | -0.1 | Percent |
| 2014 | 4.4 | 0 | Percent |
| 2015 | 4.4 | 0 | Percent |
| 2016 | 4.4 | 0 | Percent |
| 2017 | 4.4 | 0 | Percent |
| 2018 | 4.3 | -0.1 | Percent |
| 2019 | 4.3 | 0 | Percent |
| 2020 | 4.3 | 0 | Percent |