| Value | Category | Cases | |
|---|---|---|---|
| 1965 | 1 | 
                                    
                                    0.3%
                                 | |
| 1966 | 1 | 
                                    
                                    0.3%
                                 | |
| 1968 | 2 | 
                                    
                                    0.6%
                                 | |
| 1969 | 2 | 
                                    
                                    0.6%
                                 | |
| 1971 | 1 | 
                                    
                                    0.3%
                                 | |
| 1972 | 1 | 
                                    
                                    0.3%
                                 | |
| 1974 | 2 | 
                                    
                                    0.6%
                                 | |
| 1975 | 2 | 
                                    
                                    0.6%
                                 | |
| 1976 | 1 | 
                                    
                                    0.3%
                                 | |
| 1977 | 1 | 
                                    
                                    0.3%
                                 | |
| 1979 | 4 | 
                                    
                                    1.2%
                                 | |
| 1980 | 4 | 
                                    
                                    1.2%
                                 | |
| 1981 | 6 | 
                                    
                                    1.8%
                                 | |
| 1982 | 9 | 
                                    
                                    2.7%
                                 | |
| 1983 | 5 | 
                                    
                                    1.5%
                                 | |
| 1984 | 4 | 
                                    
                                    1.2%
                                 | |
| 1985 | 6 | 
                                    
                                    1.8%
                                 | |
| 1986 | 5 | 
                                    
                                    1.5%
                                 | |
| 1987 | 5 | 
                                    
                                    1.5%
                                 | |
| 1988 | 6 | 
                                    
                                    1.8%
                                 | |
| 1989 | 6 | 
                                    
                                    1.8%
                                 | |
| 1990 | 4 | 
                                    
                                    1.2%
                                 | |
| 1991 | 2 | 
                                    
                                    0.6%
                                 | |
| 1992 | 4 | 
                                    
                                    1.2%
                                 | |
| 1993 | 3 | 
                                    
                                    0.9%
                                 | |
| 1994 | 4 | 
                                    
                                    1.2%
                                 | |
| 1995 | 5 | 
                                    
                                    1.5%
                                 | |
| 1996 | 5 | 
                                    
                                    1.5%
                                 | |
| 1997 | 4 | 
                                    
                                    1.2%
                                 | |
| 1998 | 3 | 
                                    
                                    0.9%
                                 | |
| 1999 | 9 | 
                                    
                                    2.7%
                                 | |
| 2000 | 8 | 
                                    
                                    2.4%
                                 | |
| 2001 | 9 | 
                                    
                                    2.7%
                                 | |
| 2002 | 16 | 
                                    
                                    4.7%
                                 | |
| 2003 | 17 | 
                                    
                                    5%
                                 | |
| 2004 | 16 | 
                                    
                                    4.7%
                                 | |
| 2005 | 30 | 
                                    
                                    8.8%
                                 | |
| 2006 | 22 | 
                                    
                                    6.5%
                                 | |
| 2007 | 22 | 
                                    
                                    6.5%
                                 | |
| 2008 | 26 | 
                                    
                                    7.7%
                                 | |
| 2009 | 22 | 
                                    
                                    6.5%
                                 | |
| 2010 | 12 | 
                                    
                                    3.5%
                                 | |
| 2011 | 12 | 
                                    
                                    3.5%
                                 | |
| 2012 | 8 | 
                                    
                                    2.4%
                                 | |
| 2013 | 1 | 
                                    
                                    0.3%
                                 | |
| 9998 | 9998. Don't know | 0 | 
                                    
                                    0%
                                 | 
| 9999 | 9999. Missing | 1 | 
                                    
                                    0.3%
                                 |