| Value | Category |
|---|---|
| -9 | Don't know (spontaneous) |
| -8 | Refusal (spontaneous) |
| -7 | Does not apply |
| 1887 | |
| 1900 | |
| 1916 | |
| 1975 | |
| 1978 | |
| 1980 | |
| 1981 | |
| 1982 | |
| 1983 | |
| 1984 | |
| 1985 | |
| 1988 | |
| 1990 | |
| 1991 | |
| 1992 | |
| 1993 | |
| 1994 | |
| 1995 | |
| 1996 | |
| 1997 | |
| 1998 | |
| 1999 | |
| 2000 | |
| 2001 | |
| 2002 | |
| 2003 | |
| 2004 | |
| 2005 | |
| 2006 | |
| 2007 | |
| 2008 | |
| 2009 | |
| 2010 | |
| 2011 | |
| 2012 | |
| 2013 | |
| 2014 |