| Value | Category |
|---|---|
| -9 | don't know |
| -8 | refused to answer |
| -7 | not applicable |
| -6 | still in process |
| -5 | application denied |
| -4 | skipped |
| -3 | not provided |
| 1960 | |
| 1962 | |
| 1967 | |
| 1973 | |
| 1975 | |
| 1976 | |
| 1977 | |
| 1980 | |
| 1982 | |
| 1984 | |
| 1985 | |
| 1987 | |
| 1988 | |
| 1989 | |
| 1990 | |
| 1991 | |
| 1992 | |
| 1993 | |
| 1994 | |
| 1995 | |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | |
| 2000 | |
| 2001 | |
| 2002 | |
| 2003 | |
| 2004 | |
| 2005 | |
| 2006 | |
| Sysmiss |