| year | value |
|---|---|
| 1950 | 0.0 |
| 1951 | 0.0 |
| 1952 | 0.0 |
| 1953 | 0.0 |
| 1954 | 0.0 |
| 1955 | 0.0 |
| 1956 | 0.0 |
| 1957 | 0.0 |
| 1958 | 0.0 |
| 1959 | 0.0 |
| 1960 | 0.0 |
| 1961 | 0.0 |
| 1962 | 0.0 |
| 1963 | 0.0 |
| 1964 | 1.0 |
| 1965 | 2.0 |
| 1966 | 4.0 |
| 1967 | 8.0 |
| 1968 | 15.0 |
| 1969 | 27.0 |
| 1970 | 50.0 |
| 1971 | 98.0 |
| 1972 | 146.0 |
| 1973 | 171.0 |
| 1974 | 601.0 |
| 1975 | 862.0 |
| 1976 | 1431.0 |
| 1977 | 2137.0 |
| 1978 | 3540.0 |
| 1979 | 4389.0 |
| 1980 | 4312.0 |
| 1981 | 8418.0 |
| 1982 | 10695.0 |
| 1983 | 17298.0 |
| 1984 | 21881.0 |
| 1985 | 29473.0 |
| 1986 | 44831.0 |
| 1987 | 46453.0 |
| 1988 | 78744.0 |
| 1989 | 111337.0 |
| 1990 | 145990.0 |
| 1991 | 154900.0 |
| 1992 | 124138.0 |
| 1993 | 155581.0 |
| 1994 | 202459.0 |
| 1995 | 261522.0 |
| 1996 | 297557.0 |
| 1997 | 332581.0 |
| 1998 | 360806.0 |
| 1999 | 425154.0 |
| 2000 | 440061.0 |
| 2001 | 436103.0 |
| 2002 | 462495.0 |
| 2003 | 509544.0 |
| 2004 | 563815.0 |
| 2005 | 586512.0 |
| 2006 | 629888.0 |
| 2007 | 744222.0 |
| 2008 | 737694.0 |
| 2009 | 862907.7 |